diff --git a/docs/_css/mkdocstrings.css b/docs/_css/mkdocstrings.css
index 572abff..851214f 100644
--- a/docs/_css/mkdocstrings.css
+++ b/docs/_css/mkdocstrings.css
@@ -42,3 +42,25 @@ a.autorefs-external::after {
 a.autorefs-external:hover::after {
   background-color: var(--md-accent-fg-color);
 }
+
+/* A "Deprecated" admonition, styled like a warning but with its own icon. */
+:root {
+  --md-admonition-icon--deprecated: url('data:image/svg+xml;charset=utf-8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M10 2h4c3.31 0 5 2.69 5 6v10.66C16.88 17.63 15.07 17 12 17s-4.88.63-7 1.66V8c0-3.31 1.69-6 5-6M8 8v1.5h8V8zm1 4v1.5h6V12zM3 22v-.69c2.66-1.69 10.23-5.47 18-.06V22z"/></svg>');
+}
+
+.md-typeset .admonition.deprecated,
+.md-typeset details.deprecated {
+  border-color: #cc9900;
+}
+
+.md-typeset .deprecated > .admonition-title,
+.md-typeset .deprecated > summary {
+  background-color: #cc99001a;
+}
+
+.md-typeset .deprecated > .admonition-title::before,
+.md-typeset .deprecated > summary::before {
+  background-color: #cc9900;
+  -webkit-mask-image: var(--md-admonition-icon--deprecated);
+  mask-image: var(--md-admonition-icon--deprecated);
+}
diff --git a/mkdocs.yml b/mkdocs.yml
index d839d3d..d69c365 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -101,6 +101,10 @@ plugins:
         python:
           paths: ["src"]
           options:
+            extensions:
+            - griffe_warnings_deprecated:
+                kind: deprecated
+                title: Deprecated
             docstring_section_style: spacy
             inherited_members: true
             merge_init_into_class: false
diff --git a/pyproject.toml b/pyproject.toml
index 672e977..2ea7884 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -57,6 +57,7 @@ dev-formatting = ["black == 26.5.1", "isort == 9.0.1"]
 dev-mkdocs = [
   "Markdown == 3.10.3",
   "black == 26.5.1",
+  "griffe-warnings-deprecated == 1.1.1",
   "mike == 2.2.0",
   "mkdocs-gen-files == 0.6.1",
   "mkdocs-literate-nav == 0.6.3",
diff --git a/src/frequenz/core/math.py b/src/frequenz/core/math.py
index 2d1bb88..151f306 100644
--- a/src/frequenz/core/math.py
+++ b/src/frequenz/core/math.py
@@ -45,9 +45,9 @@ def __lt__(self, other: Self, /) -> bool:
 )
 """Type variable for a value that is [`LessThanComparable`][..LessThanComparable] or `None`.
 
-Warning: Deprecated
-    This type variable is deprecated and it will be removed in a future version. Use
-    [`LessThanComparableT`][..LessThanComparableT] instead.
+Deprecated:
+    This type variable is deprecated since v1.4.0 and it will be removed in a
+    future version. Use [`LessThanComparableT`][..LessThanComparableT] instead.
 """