diff --git a/src/signs_func.h b/src/signs_func.h
--- a/src/signs_func.h
+++ b/src/signs_func.h
@@ -11,7 +11,6 @@ extern SignID _new_sign_id;
 
 void UpdateAllSignVirtCoords();
 void PlaceProc_Sign(TileIndex tile);
-void MarkSignDirty(Sign *si);
 void UpdateSignVirtCoords(Sign *si);
 
 /* signs_gui.cpp */