I believe this is an old Hot Shot three finger release. It has a small Allen bolt that ajusts the trigger tension. The brown loop goes though your D loop and then around the small peg.When released the peg pivots and releases the brown loop. I got it from my Dad who bought it when he was 17 and he is now 46.
You guys just confirmed me....I was going to keep it anyhow considering I got it from my Dad and all. I still shoot with it every once in a while when I'm feeling weird.