As you may have seen in the Gallery of Projects, I make a lot of military challenge coin display racks (coin racks, challenge coin racks, coin displays). There is a history behind the Military Challenge Coin. Ask any member of the military and they will usually be able to pull a coin out of their pocket on the spot. The USO recently published a blog discussing the significance of challenge coins. You can read that article at this link:
Here is more behind the history of the Challenge Coin:
I have a rather large collection of coins. Many will never be given or traded away because they have a specific meaning or memory and were given to me personally. Others I collect because of their meaning, unit, or great design. The world of challenge coins has risen to a new level with pages dedicated to the fundraiser sale, trading of challenege coins. Each unit can create their own coin that represents the heritage, history, or special event meaning.
The coin I give with projects is a challenge coin. On the front is my Penguin inside a saw blade. On the back is a block plane, a sign of woodworking and my Navy Chief Anchor, denoting my time in the Navy as a Chief Petty Officer. Each new project purchased is accompanied by one of these coins as my way of saying thank you!