BoneFrog Legacy Group Collector Series CoinLarge 2. 5" Antique Brass Display Coins There are many examples of traditions that build camaraderie in the military, but few are as respected as the practice of carrying a challenge coin. A challenge coin is a small, decorated medallion that signifies a person is a member of a particular organization or team. Attention to detail is a key element of every military operation and its no different with how we approached the creation of this unique token.