Challenge Coins have become the number one souvenir collectable for the U.S. military. Almost every unit now has its own coin. Many officers have their coins to awards when they feel a soldier needs that "on the spot" recognition. Soldiers as far back as Korea would "Challenge" comrades by showing their coin. The Challenged soldier would have to present his coin or "buy a round". If the challenged solder had the required coins, the challenger would be required to by the round. Little has changed today