The umbrella tells the truth!

Room 8: Umbrella tip is hidden, and handle is shaped like L (12th letter).

Room 10: Umbrella points to 41.

Room 42: If the three objects in the umbrella stand represent the doors on the facing wall, the umbrella corresponds to 4.

The only other umbrella in MAZE is in the Prologue.

* Edit: Do I think these are good solutions? Not really. *