Paramedic Prayer Coin | Black Helmet Challenge Coin This makes a great gift for your favorite paramedic, 1.75 inch coin in a collector plastic case for protection. The coin is made with great quality detail, antique hand polish silver finish with enamel. Here is my favorite version of the history of the Challenge Coin. In WWI a particular Allied squadron all wore the same bronze medallion. Some pilots just carried it in their pockets like coins. One of them was shot down behind enemy lines and captured. He later escaped and was captured by his own allied forces. With no identification, he was going to be executed as a saboteur, but one of the officers recognized his medallion.