Richard Garriott's Tabula Rasa (Limited Collector's Edition)

The "Challenge" coin is used in a little game invented by Richard Garriott. The idea is that you can take this coin and challenge anyone. If the challenged can't answer the challenge with his own "Challenge" coin, he looses and needs to buy you a drink but if he has the coin on him, you'll be the one who needs to open up the wallet.