I'm going to say this then I'm going to bow out of this discussion but if you bought it, it's not a Challenge Coin. It's a souvenir.
Challenge Coins started out as a Military tradition. They were given for exemplary performance that didn't quite merit an AAM. (Army Achievement Medal).
They started calling them "Challenge" coins because apparently there was a tradition that when service members met at a bar somebody would throw their coin on the table as a challenge and everybody else at the table had to produce one too. If you couldn't you had to buy the next round. If everybody at the table had one the person who initially threw theirs down had to buy the next round.
Like many other Military traditions Challenge Coins have been appropriated by various police departments.
Enjoy your discussion folks