This beautiful silver nickel 2" coin is designed with the CKFF logo in black on one side and an American Flag detail in black on the reverse side. Challenge coins originated during World War I. They were issued to battalions as symbols of camaraderie and unity. Later, they were used as a way of verifying membership in a club, group or military unit. We are making this available to you as a supporter of the Chris Kyle Frog Foundation.