The game that inspired Code 777, this one involves deducing the 3 letter cards that you wear in a band strapped to your head. Unlike Code 777 there are no colors involved just the 6 letters A, B,C,D,E & G. (Note: there even exists a version with number cards: What's That on My Head?)
On your turn you ask a question aloud and then answer it. The questions involve the letters you can see on your opponent's heads, like sums, odds vs. evens, etc. The questions on each card are ranked in difficulty so you can vary the difficulty depending on the participants.
Using the answers to the question you race to deduce your letter. If you get it wrong you keep the three letters, but lose 4 points. If you get it right you get 10 points and 3 new letters on your head. First person to some set total wins.
Similar to:
Code 777
Amnesia
Egghead
What's That on My Head?
Guess What I Am!
Coyote
Pow Wow
Am I a Banana?