I took this one of these things up to folks around the range and asked them what they figured it was for. Nobody got it. (It wasn't attached to the arrow at the time. I guess that's relevant.) It's an FOB - a 'fletching only better'. I can't vouch for that myself but it's definitely a curio. It's designed to stay behind to mark your spot, if your arrow passes through the target.
Mostly, I was digging the company of the trio who were zinging these down the range. Again with the guessing games, if you'd asked I would have guessed they were family but it was a fun guy named Phillip with a couple of youthful church-mates. He's into archery and one of the kids who helps out there was excited about it, so with the mom's permission, the kid and his sis got to give the bow a go. They were having a great time, and they were a very sociable bunch. I offered to help them do the search in the grass for stuff that went past, and Phillip offered to get the FOB guy on the phone! Alas, no answer, so the joke was on us.
Thanks to Henry Zhu, who just happened to be nearby with a fancy camera, so I said, "Hey, can you take a pretty picture of those and send it to me?" It is pretty, Henry!