diff --git a/addons/mail/models/mail_thread.py b/addons/mail/models/mail_thread.py
index 60acd6b7416..54fb13ad08f 100644
--- a/addons/mail/models/mail_thread.py
+++ b/addons/mail/models/mail_thread.py
@@ -22,6 +22,7 @@ from email import message_from_string, policy
 from lxml import etree
 from werkzeug import urls
 from xmlrpc import client as xmlrpclib
+from markupsafe import Markup
 
 from odoo import _, api, exceptions, fields, models, tools, registry, SUPERUSER_ID, Command
 from odoo.exceptions import MissingError
@@ -2400,8 +2401,8 @@ class MailThread(models.AbstractModel):
             author_user = self.env.user if self.env.user.partner_id == author else author.user_ids[0] if author and author.user_ids else False
             if author_user:
                 signature = author_user.signature
-            else:
-                signature = "<p>-- <br/>%s</p>" % author.name
+            elif author.name:
+                signature = Markup("<p>-- <br/>%s</p>") % author.name
 
         if force_email_company:
             company = force_email_company
diff --git a/addons/test_mail/tests/test_message_post.py b/addons/test_mail/tests/test_message_post.py
index 98a25c61c95..71352d2d5da 100644
--- a/addons/test_mail/tests/test_message_post.py
+++ b/addons/test_mail/tests/test_message_post.py
@@ -15,6 +15,8 @@ from odoo.tests import tagged
 from odoo.tools import mute_logger, formataddr
 from odoo.tests.common import users
 
+from markupsafe import escape
+
 
 @tagged('mail_post')
 class TestMessagePost(TestMailCommon, TestRecipients):
@@ -108,6 +110,18 @@ class TestMessagePost(TestMailCommon, TestRecipients):
         self.assertNotIn(signature, found_mail.body_html)
         self.assertEqual(found_mail.body_html.count(signature), 0)
 
+    @users('employee')
+    def test_notify_by_email_add_signature_no_author_user_or_no_user(self):
+        self.test_message.author_id = self.env['res.partner'].sudo().create({
+            'name': 'Steve',
+        }).id
+        template_values = self.test_record._notify_by_email_prepare_rendering_context(self.test_message, {})
+        self.assertNotEqual(escape(template_values['signature']), escape('<p>-- <br/>Steve</p>'))
+
+        self.test_message.author_id = None
+        template_values = self.test_record._notify_by_email_prepare_rendering_context(self.test_message, {})
+        self.assertEqual(template_values['signature'], '')
+
     @users('employee')
     def test_notify_by_email_prepare_rendering_contextt(self):
         """ Verify that the template context company value is right