Challenge coins have been proliferating in recent years, due to decreasing costs among other reasons.
Information can be found in this article -http://www.washingtonpost.com/wp-dyn/content/article/2009/11/01/AR2009110102261.html
We have an extremely large, but not well-catalogued, numismatics collection occupying a couple of safes in Historical Collections. To better position the Museum for the long-term addition of these to the numismatics collection, I’ve proposed that we scan the ones that people have on their desks, and record who was giving the coin out and when. I did the ones on my desk this morning