I figured it was a shell game. About ten years ago, I know there were some guys on BART running a shell game, which was a con artist's trick. Specifically, they'd start to play, and then when someone pulled out a wallet to bet, they'd grab the wallet and run. I managed to outsmart them by having no money. Anyway, I walked on warily.
A friend of mine told me more - he saw the same guy later in the afternoon, and approached. It wasn't a shell game. The "shells" were large, round-topped beetles, very affectionate, with ornamental paintings on the backs. One had a happy face, another one had an anarchy sign, and a last one was waiting for you.
So, you should go pick it up. My friend didn't tell me -- out of curiosity, what did your beetle have painted on the back?