When FenchurchE and I (NepoKama) were heading out to try Geocaching for the first time we were talking about what we'd read about our soon-to-be addiction. At one point in the conversation she said "I've read about these things called Geocoins. I hear you can design your own and I know exactly what I'd want to do!" My immediate reply was "A brass cannon on a field of sable with stars and a red bar-sinister with the word TANSTAAFL across the bottom?"

For those who don't recognize the reference, that's the flag of Free Luna from her favorite book, The Moon is a Harsh Mistress by Robert Heinlein.  The coin was created as a gift for FenchurchE in 2012. The reverse features a map of the moon with locations from the book.