Lord Judas said:Since he wont give out the answer post-game, lump me into the crowd that thinks he either made a major blunder presenting it (like a few messed up symbols), -or- he plans on using it, or a variant of it, in the future <shudder>.
Regardless of past performance, not fessing up once the books are packed up is pretty cruel.
My solution is simplicity itself: Have someone else in the group start a campaign. After character creation, the players are told that their characters are locked in a room. There's no food or water. The only way out is to solve a puzzle...with circles...and double arrows...and upside-down triangles.
Either the ex-GM produces the solution, or the campaign ends. Rinse and repeat until the ex-GM gives the solution or he fesses up and admits there isn't one.