oops. Challenge coin.
They have NEVER been given or exchanged in a note passing fashion. In fact, all but one, my retirement COIN from Commander, USSOCOM, were given in a ceremony so everyone present knew I had the coin. That public knowledge is important because, if you are challenged to produce a coin and don't have one you expected to “buy the bar” for everyone who can produce their own coin.
The USSOCOM Coin was presented to me upon my retirement by my squadron commander at my retirement ceremony. he also read the accompanying letter. It was a surprise to him and to almost everyone who attended that ceremony, Friday 13 April, 1990.