CHALLENGE COINS
A challenge coin is a small coin or medallion bearing an organization’s insignia or emblem and carried by members. Traditionally, they are given to prove membership when challenged and to enhance morale. In addition, they are also collected by military service members. In practice, one member 'challenges' another by presenting their coin, and if the challenged member does not have their coin on their person, they are subjected to a consequence (usually picking up the tab for drinks).