[sexobon]

I'm surprised Challenge Coins haven't replaced class rings on a large scale:

… In the context as they are used by the modern U.S. military, the tradition probably began among special forces units during the Vietnam War. The tradition spread through the Airborne community, and by the early 1980s also into the 75th Ranger Regiment. …

… Challenge coins are also exchanged outside the military. NASCAR, the NFL, cadets of the Civil Air Patrol, Eagle Scouts and World Series of Poker all have their own challenge coins. They are also becoming popular with police departments, fire departments and fraternal organizations. In 2007, the Utah Symphony and Opera gave challenge coins to all of its staff and musicians, making it the first symphony organization in America to do so. Franklin Public School in Ontario has a coin that is given to graduates, featuring its mascot 'Frankie'. …

… As of 2010, coins manufactured in China and South Korea typically cost between US$2.50 to US$7.00 per coin, depending on production process and complexity of design, laser engraving, enamels, voids, etc. The dies must be sculpted by an artist and can range in cost from US$50 to US$300, depending on complexity. The cost of domestic manufacture can be many times this amount.

In order to be competitive, most North American companies offering challenge coins rely on having the product manufactured offshore. Many challenge coins are fabricated in South Korea, as the connection to the US military bases there is strong, and costs are cheaper than those made in the US. ...

Some entertaining stories from the linked Wiki article here.