--- a/hgext3rd/topic/stack.py	Fri Aug 26 14:58:18 2016 +0200
+++ b/hgext3rd/topic/stack.py	Fri Aug 26 14:14:04 2016 +0200
@@ -2,6 +2,7 @@
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
+from mercurial.i18n import _
 from mercurial import (
     destutil,
     error,
@@ -19,6 +20,14 @@
     prev = None
     entries = []
     idxmap = {}
+
+    label = 'topic'
+    if topic == repo.currenttopic:
+        label = 'topic.active'
+
+    fm.plain(_('### topic: %s\n') % ui.label(topic, label),
+             label='topic.stack.summary.topic')
+
     for idx, r in enumerate(getstack(repo, topic), 1):
         ctx = repo[r]
         p1 = ctx.p1()

--- a/tests/test-topic-stack-data.t	Fri Aug 26 14:58:18 2016 +0200
+++ b/tests/test-topic-stack-data.t	Fri Aug 26 14:14:04 2016 +0200
@@ -240,6 +240,7 @@
 =======================================
 
   $ hg stack bar
+  ### topic: bar
   t5: add bar_c
   t2^ add bar_b (base)
   t4$ add bar_e (unstable)
@@ -248,14 +249,17 @@
   t1: add bar_a
     ^ add base_e
   $ hg stack baz
+  ### topic: baz
   t2: add baz_b
   t1: add baz_a
     ^ add base_c
   $ hg stack foo
+  ### topic: foo
   t2@ add foo_b (current)
   t1: add foo_a
     ^ add lake_a
   $ hg stack fuz
+  ### topic: fuz
   t3$ add fuz_c (unstable)
   t2$ add fuz_b (unstable)
   t1: fuz1_a

--- a/tests/test-topic-stack.t	Fri Aug 26 14:58:18 2016 +0200
+++ b/tests/test-topic-stack.t	Fri Aug 26 14:14:04 2016 +0200
@@ -53,6 +53,7 @@
   switching to topic other
   0 files updated, 0 files merged, 4 files removed, 0 files unresolved
   $ hg topic --list
+  ### topic: other
   t2@ c_b (current)
   t1: c_a
   $ hg phase --public 'topic("other")'
@@ -68,6 +69,7 @@
   $ hg topic
    * foo
   $ hg stack
+  ### topic: foo
   t4@ c_f (current)
   t3: c_e
   t2: c_d
@@ -124,6 +126,7 @@
   o  0 default {} public c_a
   
   $ hg topic --list
+  ### topic: foo
   t4$ c_f (unstable)
   t3$ c_e (unstable)
   t2@ c_d (current)
@@ -192,6 +195,7 @@
 Test output
 
   $ hg top -l
+  ### topic: foo
   t6: c_f
   t5: c_e
   t2^ c_d (base)
@@ -234,6 +238,7 @@
   
 
   $ hg topic --list
+  ### topic: foo
   t6$ c_f (unstable)
   t5$ c_e (unstable)
   t2^ c_D (base)