diff --git a/api/lab/get_firma_usuario.php b/api/lab/get_firma_usuario.php
new file mode 100644
index 0000000..10f7a51
--- /dev/null
+++ b/api/lab/get_firma_usuario.php
@@ -0,0 +1,16 @@
+<?php
+/**
+ * GET ?user_id=X — Devuelve la firma_svg de un usuario (solo admins).
+ */
+require_once __DIR__ . '/_helpers.php';
+requireAdmin();
+
+$userId = (int)($_GET['user_id'] ?? 0);
+if ($userId <= 0) jsonError('user_id requerido.');
+
+$db  = Database::getInstance()->getConnection();
+$row = $db->prepare("SELECT firma_svg FROM admin_users WHERE id = ? LIMIT 1");
+$row->execute([$userId]);
+$data = $row->fetch(PDO::FETCH_ASSOC);
+
+jsonOk(['firma_svg' => $data['firma_svg'] ?? null]);
diff --git a/api/lab/get_lab_users.php b/api/lab/get_lab_users.php
index 8d41b51..150c2d1 100644
--- a/api/lab/get_lab_users.php
+++ b/api/lab/get_lab_users.php
@@ -21,6 +21,7 @@ $users = $db->fetchAll("
         u.enfermera_id,
         u.last_login,
         u.created_at,
+        (u.firma_svg IS NOT NULL) AS tiene_firma,
         r.name  AS role_name,
         r.color AS role_color,
         r.slug  AS role_slug,
@@ -33,6 +34,7 @@ $users = $db->fetchAll("
 
 foreach ($users as &$u) {
     $u['is_active']   = (bool)$u['is_active'];
+    $u['tiene_firma'] = (bool)$u['tiene_firma'];
     $u['role_name']   = $u['role_name']  ?? ucfirst($u['role'] ?? 'admin');
     $u['role_color']  = $u['role_color'] ?? '#0d6efd';
 }
diff --git a/api/lab/save_firma_usuario.php b/api/lab/save_firma_usuario.php
new file mode 100644
index 0000000..9488f61
--- /dev/null
+++ b/api/lab/save_firma_usuario.php
@@ -0,0 +1,28 @@
+<?php
+/**
+ * POST — Admin guarda/borra la firma pre-configurada de cualquier usuario.
+ * Body JSON: { user_id: 5, firma_svg: "data:image/png;base64,..." }
+ *            { user_id: 5, _borrar: true }
+ */
+require_once __DIR__ . '/_helpers.php';
+requireAdmin();
+
+$body   = json_decode(file_get_contents('php://input'), true) ?? [];
+$userId = (int)($body['user_id'] ?? 0);
+if ($userId <= 0) jsonError('user_id requerido.');
+
+$db = Database::getInstance()->getConnection();
+
+if (!empty($body['_borrar'])) {
+    $db->prepare("UPDATE admin_users SET firma_svg = NULL WHERE id = ?")->execute([$userId]);
+    jsonOk(['mensaje' => 'Firma eliminada.']);
+}
+
+$svg = $body['firma_svg'] ?? '';
+if (strlen($svg) < 100) jsonError('Firma requerida.');
+if (!preg_match('/^data:image\/(svg\+xml|png|jpeg|webp);base64,/i', $svg)) {
+    jsonError('Formato de firma no válido.');
+}
+
+$db->prepare("UPDATE admin_users SET firma_svg = ? WHERE id = ?")->execute([$svg, $userId]);
+jsonOk(['mensaje' => 'Firma guardada correctamente.']);
diff --git a/lab_usuarios.php b/lab_usuarios.php
index b5be092..86dfcf4 100644
--- a/lab_usuarios.php
+++ b/lab_usuarios.php
@@ -210,6 +210,56 @@ require_once __DIR__ . '/shared/components/sidebar.php';
     </div>
 </div>
 
+<!-- ══════════════════════════════════════════════════════════
+     MODAL — FIRMA DE USUARIO
+══════════════════════════════════════════════════════════ -->
+<div class="modal fade" id="modalFirmaUsuario" tabindex="-1" aria-hidden="true">
+    <div class="modal-dialog">
+        <div class="modal-content">
+            <div class="modal-header">
+                <h5 class="modal-title"><i class="fas fa-signature me-2"></i>Firma de <span id="firma-u-nombre"></span></h5>
+                <button type="button" class="btn-close" data-bs-dismiss="modal"></button>
+            </div>
+            <div class="modal-body">
+                <input type="hidden" id="firma-u-id">
+
+                <!-- Firma actual -->
+                <div id="firma-u-actual" class="mb-3 d-none">
+                    <label class="form-label small fw-semibold text-muted">Firma guardada</label>
+                    <div class="border rounded p-2 text-center bg-light">
+                        <img id="firma-u-img" src="" alt="Firma" style="max-height:80px;max-width:100%">
+                    </div>
+                    <button class="btn btn-outline-danger btn-sm mt-2 w-100" onclick="firmaUsuario.borrar()">
+                        <i class="fas fa-trash me-1"></i>Eliminar firma guardada
+                    </button>
+                </div>
+
+                <!-- Canvas para dibujar -->
+                <label class="form-label small fw-semibold">Dibujar nueva firma</label>
+                <div style="border:1px solid #dee2e6;border-radius:8px;background:#fff;touch-action:none">
+                    <canvas id="firma-u-canvas" width="460" height="140" style="width:100%;height:140px;border-radius:8px;cursor:crosshair"></canvas>
+                </div>
+                <div class="d-flex gap-2 mt-2">
+                    <button class="btn btn-outline-secondary btn-sm" onclick="firmaUsuario.limpiarCanvas()">
+                        <i class="fas fa-eraser me-1"></i>Limpiar
+                    </button>
+                    <div class="ms-auto">
+                        <label class="form-label small fw-semibold mb-0 me-2">O subir imagen:</label>
+                        <input type="file" id="firma-u-file" accept="image/*" class="form-control form-control-sm d-inline-block" style="width:auto" onchange="firmaUsuario.cargarImagen(this)">
+                    </div>
+                </div>
+                <div class="alert alert-danger mt-2 d-none" id="firma-u-error"></div>
+            </div>
+            <div class="modal-footer">
+                <button class="btn btn-secondary" data-bs-dismiss="modal">Cancelar</button>
+                <button class="btn btn-primary" onclick="firmaUsuario.guardar()">
+                    <i class="fas fa-save me-1"></i>Guardar firma
+                </button>
+            </div>
+        </div>
+    </div>
+</div>
+
 <!-- ══════════════════════════════════════════════════════════
      MODAL — ROL
 ══════════════════════════════════════════════════════════ -->
@@ -460,6 +510,11 @@ const usuarios = {
                 <td class="text-muted small">${lastLogin}</td>
                 <td class="text-end table-actions">
                     <button class="btn btn-sm btn-outline-primary" onclick="usuarios.editar(${u.id})"><i class="fas fa-edit"></i></button>
+                    <button class="btn btn-sm ${u.tiene_firma ? 'btn-success' : 'btn-outline-secondary'} ms-1"
+                            onclick="firmaUsuario.abrir(${u.id}, '${esc(u.full_name ?? u.username)}')"
+                            title="${u.tiene_firma ? 'Ver / cambiar firma' : 'Subir firma'}">
+                        <i class="fas fa-signature"></i>
+                    </button>
                     <button class="btn btn-sm btn-outline-danger ms-1" onclick="usuarios.eliminar(${u.id},'${esc(u.username)}')"><i class="fas fa-trash-alt"></i></button>
                 </td>
             </tr>`;
@@ -596,6 +651,142 @@ document.getElementById('r_slug').addEventListener('input', function() {
     }
 })();
 </script>
+
+<script>
+// ── Gestión de firma por usuario ────────────────────────────
+const firmaUsuario = (() => {
+    let _canvas, _ctx, _drawing = false;
+
+    function initCanvas() {
+        _canvas = document.getElementById('firma-u-canvas');
+        _ctx    = _canvas.getContext('2d');
+        _ctx.strokeStyle = '#1e293b';
+        _ctx.lineWidth   = 2.2;
+        _ctx.lineCap     = 'round';
+
+        const pos = e => {
+            const r = _canvas.getBoundingClientRect();
+            const t = e.touches?.[0] ?? e;
+            return [(t.clientX - r.left) * (_canvas.width / r.width),
+                    (t.clientY - r.top)  * (_canvas.height / r.height)];
+        };
+        const start = e => { e.preventDefault(); _drawing = true; _ctx.beginPath(); _ctx.moveTo(...pos(e)); };
+        const move  = e => { e.preventDefault(); if (!_drawing) return; _ctx.lineTo(...pos(e)); _ctx.stroke(); };
+        const stop  = ()  => { _drawing = false; };
+
+        _canvas.addEventListener('mousedown',  start);
+        _canvas.addEventListener('mousemove',  move);
+        _canvas.addEventListener('mouseup',    stop);
+        _canvas.addEventListener('mouseleave', stop);
+        _canvas.addEventListener('touchstart', start, { passive: false });
+        _canvas.addEventListener('touchmove',  move,  { passive: false });
+        _canvas.addEventListener('touchend',   stop);
+    }
+
+    return {
+        abrir(userId, nombre) {
+            document.getElementById('firma-u-id').value    = userId;
+            document.getElementById('firma-u-nombre').textContent = nombre;
+            document.getElementById('firma-u-error').classList.add('d-none');
+            document.getElementById('firma-u-file').value = '';
+
+            // Mostrar firma actual si existe
+            const u = (typeof allUsers !== 'undefined' ? allUsers : []).find(x => x.id === userId);
+            const actualEl = document.getElementById('firma-u-actual');
+            if (u?.tiene_firma) {
+                // Cargar imagen desde servidor
+                fetch(`api/lab/get_firma_usuario.php?user_id=${userId}`)
+                    .then(r => r.json())
+                    .then(j => {
+                        if (j.firma_svg) {
+                            document.getElementById('firma-u-img').src = j.firma_svg;
+                            actualEl.classList.remove('d-none');
+                        }
+                    }).catch(() => {});
+            } else {
+                actualEl.classList.add('d-none');
+            }
+
+            if (!_canvas) initCanvas();
+            this.limpiarCanvas();
+            new bootstrap.Modal('#modalFirmaUsuario').show();
+        },
+
+        limpiarCanvas() {
+            if (_ctx) _ctx.clearRect(0, 0, _canvas.width, _canvas.height);
+        },
+
+        cargarImagen(input) {
+            const file = input.files[0];
+            if (!file) return;
+            const reader = new FileReader();
+            reader.onload = e => {
+                const img = new Image();
+                img.onload = () => {
+                    if (!_canvas) initCanvas();
+                    this.limpiarCanvas();
+                    const scale = Math.min(_canvas.width / img.width, _canvas.height / img.height);
+                    const w = img.width * scale, h = img.height * scale;
+                    _ctx.drawImage(img, (_canvas.width - w) / 2, (_canvas.height - h) / 2, w, h);
+                };
+                img.src = e.target.result;
+            };
+            reader.readAsDataURL(file);
+        },
+
+        async guardar() {
+            const userId = parseInt(document.getElementById('firma-u-id').value);
+            const errEl  = document.getElementById('firma-u-error');
+            errEl.classList.add('d-none');
+
+            // Verificar que el canvas tenga algo dibujado
+            const blank = document.createElement('canvas');
+            blank.width = _canvas.width; blank.height = _canvas.height;
+            if (_canvas.toDataURL() === blank.toDataURL()) {
+                errEl.textContent = 'Dibuja o sube una firma primero.';
+                errEl.classList.remove('d-none');
+                return;
+            }
+
+            const png = _canvas.toDataURL('image/png');
+            try {
+                const res  = await fetch('api/lab/save_firma_usuario.php', {
+                    method: 'POST', headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ user_id: userId, firma_svg: png })
+                });
+                const json = await res.json();
+                if (!json.ok) { errEl.textContent = json.error || 'Error'; errEl.classList.remove('d-none'); return; }
+                bootstrap.Modal.getInstance(document.getElementById('modalFirmaUsuario'))?.hide();
+                // Marcar tiene_firma en memoria local para actualizar el botón
+                if (typeof allUsers !== 'undefined') {
+                    const u = allUsers.find(x => x.id === userId);
+                    if (u) u.tiene_firma = true;
+                    if (typeof usuarios !== 'undefined') usuarios.render();
+                }
+            } catch (e) { errEl.textContent = 'Error de conexión.'; errEl.classList.remove('d-none'); }
+        },
+
+        async borrar() {
+            const userId = parseInt(document.getElementById('firma-u-id').value);
+            if (!confirm('¿Eliminar la firma guardada de este usuario?')) return;
+            try {
+                const res  = await fetch('api/lab/save_firma_usuario.php', {
+                    method: 'POST', headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ user_id: userId, _borrar: true })
+                });
+                const json = await res.json();
+                if (!json.ok) return;
+                document.getElementById('firma-u-actual').classList.add('d-none');
+                if (typeof allUsers !== 'undefined') {
+                    const u = allUsers.find(x => x.id === userId);
+                    if (u) u.tiene_firma = false;
+                    if (typeof usuarios !== 'undefined') usuarios.render();
+                }
+            } catch (_) {}
+        }
+    };
+})();
+</script>
 <script src="assets/js/lab-sidebar.js"></script>
 </body>
 </html>