Unless you are employed in the military or in the government, you might not have heard of or even issued a 'Challenge Coin', but they are very popular among military and government people especially in the USA where there is a strong ongoing tradition behind them. To be precise, some challenge coins are so valued that owners never part with them and even if they sell, they command very expensive prices. This is the reason why there is a very big market for them and a lot of organizations now even commercial ones are issuing them. If you're primarily into old coins and medals collecting, perhaps it might be time to take a look at challenge coins...