Over a dozen postcards (the precise number is revealed only to the participants), each featuring a different Kcymaerxthaere marker. Each card is stamped and postmarked from a post office near the featured plaque site on the card. Each card reveals new clues to help solve the Kcy puzzle. Winner will receive a grand prize. (If you purchase this item, all past cards will be sent to bring you current to receive the next card.) We have a nice little group going on Flickr. People photograph the cards in many different surroundings.
Notice on the second photo here, you can see mysterious information on the back of the card. There is some on all the cards and they add up to a mystery and an answer.