To be honest, they literally come in all shapes and sized.  You just have to do a lot of research...almost all will have eep roms in them (they are the black IC chips with clear windows in them), but the label could be anything.  I have an early build of Caveman Games that   has a generic white sticker (that says Caveman Games and the date) over the top of a Cobra Command label just for an example of an oddity.