A challenge coin is a small, coin-like object that typically bears the emblem or insignia of an organization, unit, or individual. These coins are often used in the military but have expanded to other groups and institutions. The tradition of challenge coins has a rich history and involves a set of customs and rules.

Here are some key aspects of challenge coins:

1. Origin: The exact origin of challenge coins is debated, but they are believed to have originated in the military. One popular story dates back to World War I when a wealthy lieutenant had bronze medallions struck with the squadron's emblem for his unit. One of the pilots kept the medallion in a leather pouch around his neck. Later, when he was captured by the enemy, the medallion helped him escape execution by proving his identity.

2. Design: Challenge coins typically feature a unique design specific to the organization or group they represent. They can be made of various metals, including bronze, silver, or gold. The design often includes symbols, mottos, and other elements that hold significance to the group.

3. Use in Challenges: The most well-known tradition associated with challenge coins is the "coin check" or "challenge." In this tradition, a member of the group can initiate a challenge by presenting their coin. Other members must then produce their coins. If a member is unable to do so, they may be required to perform a task or buy a round of drinks, depending on the rules established by the group.

4. Presentation: Challenge coins are often presented as a token of recognition or appreciation. They can be given to members for outstanding performance, achievements, or as a symbol of camaraderie. The act of giving or receiving a challenge coin is often accompanied by a handshake and a few words of acknowledgment.

5. Collectibility: Beyond their functional use in challenges, many people collect challenge coins. Each coin may represent a specific unit, event, or milestone, making them valuable to collectors and serving as a tangible record of an individual's or group's history.

While the tradition of challenge coins has strong roots in the military, it has expanded to other organizations, including government agencies, businesses, and non-profit groups. The exchange of challenge coins has become a symbol of belonging, camaraderie, and shared experiences.