The ingenius
copy protection scheme for
The Secret of Monkey Island, similar to
code wheels used in
Star Control,
Curse of the Azure Bonds and many other game of about the same time. Before the game started it would ask you for a word resulting from a particular combination of face segments you could align on a series of paper circles rotating around the same axis.
What's more, Dial-a-Pirate had a secret message on the inside for scurvy scumdogs who took their wheel apart to photocopy for piracy purposes!
What is it? Well, if I told you, it wouldn't be a secret anymore...