An original gas cap for the German made Isetta's. The material is bakelite with a painted aluminum emblem.
Here's another version of the Isetta gas cap. I've seen some metal reproduction caps that looked like this and didn't realize they were based on this original bakelite gas cap. I'm guessing this is an earlier version than what was on my Isetta's. As you can see from the final ebay bidding price, it was quite a hot commodity.