Have been out of the graphic design biz for some time now, but thought I'd throw a couple into the mix.

Based on the idea of exchange of goods and services (or currency "velocity" if you like).



Quick and dirty I admit.

One thing to consider is that logos should be vector-based so you're not requiring sizes to be produced by the artist in every application, as well as allowing for more attractive implementation in responsive web designs (not to mention printed materials).
Although I'm not the biggest fan, it seems current design trends are favoring flat designs - for now - so that's what I went with.

Still highly skeptical of the prospects for this project... but hey, bounty coins are easy to hold forever!