diff --git a/src/signs_cmd.cpp b/src/signs_cmd.cpp
--- a/src/signs_cmd.cpp
+++ b/src/signs_cmd.cpp
@@ -21,6 +21,7 @@
 
 #include "table/strings.h"
 
+/** The last built sign. */
 SignID _new_sign_id;
 
 /**