Since I'm more or less happy with the design now (after a few inevitable corrections), I decided to design and order a full badge now. It looks something like this:
There are python snakes on the copper layer under the large white rectangle — but you can't see them, since they are covered. I think they will still be visible in reality, due to their relief. The bottom half can be broken off — when you want to use this for something else after the conference ends.