diff --git a/src/signs_func.h b/src/signs_func.h
--- a/src/signs_func.h
+++ b/src/signs_func.h
@@ -14,7 +14,6 @@
 #include "tile_type.h"
 
 struct Window;
-extern SignID _new_sign_id;
 
 void UpdateAllSignVirtCoords();
 void PlaceProc_Sign(TileIndex tile);