The official Z4 one is too long. Its the only "freebie" I managed to grind out of my stingy stealer and I was disappointed with it, so don't use it. I use the "3" series one I have instead.
I was looking at doing exactly this a while back but had trouble finding examples that didn't look naff. The TVR one I found looks cool, but other either look too "corporate conference goody bag" or too spiky and unweildy
I would prefer something a bit more based on the forum identity so I can get them made up in bulk and sell them in the shop, alongside the stickers, rather than something unofficial for sale within a thread. If we can do it this way I can order in bulk and save us money at the same time