A couple years ago a had a great idea for making custom stamps (not an original one, mind you) and I got excited when I saw a friend's necklace. So I borrowed it and used a magic foam type product that retains the imprint of what you press into it. Then I stamped it!
Pretty cool but I didn't want the edge. So I cut out the imprint and tried again.
This is the final result. (front of the card and inside)