My husband was in the navy. He said one of the things that a lot of military units do is make coins with the unit logo and motto, some are simply metal coins and sometimes they will be in the units “colors.” He was telling me of an army tradition where if you have a unit coin and are ask to produce it if you are in a bar, you will have to produce it or buy a round of drinks. This kind of makes the coin challenge coins. When he was working with army units, he would always make sure he had that unit’s coin with him (if one had been presented to him). Now we are looking to display the various coins he obtained in his navy years. They are very nice and my daughters keep on asking to have their own.