I like the idea of retro t-shirts......or how about a range of colours with a silhouette of a cabby, coupe or touring. Or maybe some t-shirts with one of those cartoon style E30s? Again you could have a cabby, coupe, touring and so on. There are enough members who own the varous models.
The retro hot rod stickers are cool, as I love rods, but maybe more suitable for a 40s/50s ride? I think a minimalist design might be better?
