5 G's Monster "Collector" Coin
Challenge coins began to catch on during the Vietnam War. The first coins from this era were created by either the Army's 10th or 11th Special Forces Group and were little more than common currency with the unit's insignia stamped on one side, but the men in the unit carried them with pride.
Back at the squadron, it became tradition to ensure that all members carried their medallion or coin at all times. This was accomplished through challenge in the following manner: a challenger would ask to see the medallion, if the challenged could not produce a medallion, they were required to buy a drink of choice for the member who challenged them. If the challenged member produced a medallion, then the challenging member was required to pay for the drink. This tradition continued throughout the war and for many years after the war while surviving members of the squadron were still alive.