Airman's Creed Challenge Coin

•Coin measures 1¾" in diameter

The history of challenge coins goes back a long time, though the true origin is disputed. Some stories date them back as far as World War I, whereas others claim they are as recent as the Vietnam War.
The modern day challenge coin is used as a symbol of unity, as an award for meritorious behavior, and of course as a challenge. "Coin Checks", as these challenges are called, are a way to boost morale, prove membership, and, if caught without your coin, a way to end up having to buy the challenger's next round of drinks.