I am going to play a littles "Devil's Advocate" here... Did you have your name and phone number in your hat? It was left there on the trail or in the trash pile for over a week. It is a bummer to lose the pin, I lost one on a hat years ago in the mouth of the Merrimack (to dangerous to turn the boat around to go back and get it). If it in the "trash" from May 2nd-11th and someone picked off the pin, that is not stealing... Displaying it as their own would be a low life thing to do, but picking trash is not theft.
What would be the right thing to do? A "greasy" hat is lying in the "trash", it has been there for a while, maybe you have walked by it a few times, but now you see there is a bronze pin. Do you leave the pin on the hat, in the "trash"? The right thing to do would be to dispose of any trash you pick up properly and if you find something of possible value (without any way to determine who it was), maybe you bring it to the police station or maybe you keep it. Did you check with the police?
It is always a sad to loose something we care about, but I think it is clear that it was lost and not stolen. Maybe this summer you will be walking through a flea market and you will see your pin in a case and after talking with the guy selling it, you demonstrate it was yours and he had found it on the side of a trail, he then gives it to you, you never know...
I am sorry you lost your pin, I hope for a few bucks you can get another. Better yet I hope you can get a even bigger Crappy this season!