Rollerball,
RWY12 doesn't make anything, it just places already made items.

Ah Steve. Thanks for that. Yet another reason for going for SceneGenX then, that contains a fantastic and easy to use taxiway sign maker (using the XML SDK of course)

But seriously, otherwise if you only want a few taxiway signs in an existing scenery, best just to spend an evening learning how to create them directly in XML code using the scenery SDK and BGLComp. Not too difficult really.