I was happy to find your site. I graduated from MACV Recondo School in 1968. I was with the 101st (ABN) 3/506th E company (LRRP)
Army 5th Special Forces Group (Vietnam) Challenge Coin
What is a challenge coin?
Challenge coins were originally used by Special Forces to recognize soldiers for outstanding acts, team training, unit identification, to boost esprit de corps, and to build camaraderie. Today, all military and many law enforcement units have challenge coins. Traditionally, "coining" was executed to see if fellow soldiers were carrying their unit's coin. In the Viet Nam era this tradition was modified slightly so that the loser of the challenge (Not carrying a coin) was obligated to buy a round of drinks. Today Challenge Coins are handsomely presented in display cases for everyone’s enjoyment. Many people trade these coins at training and collect other department/unit coins.