How about those oval car stickers you see all over the place here in the US (derived from the country symbol stickers in Europe)... around here you see a lot of "OBX" (for "Outer Banx, NC") stickers, popular touristy things from resorts....
Anyhow, an oval "GTA" sticker would be kinda cool, I'd buy one and slap it on the old GTI with pride... or there could be GTVA, or PVN, or NTF, depending on your allegiance

Dunno what the Shivans put on the back of their minivans, maybe just a sillhoutte of a Sath...
(Another dorky idea from the guy who brought you the "GTD Galatea Athletic Department" T-Shirt)