Gustav's License is treasure that can be obtained in Sly Cooper: Age of Thieves in the episode In the Air Tonight. It is worth 238 coins and the time needed to reach the safehouse is thirty-two seconds.
"Everyone's not-so favorite flying fish, Gustav Gale, was once an ace fighter pilot working for Russia. His piloting license was permanently revoked, but it appears that he may have stolen it back. He hasn't kept much watch over it, though, as a pigeon managed to take off with it due to Gustav not paying attention or caring."
It is located in a pigeon's nest just above the enemy hangar, but it's blocked by an obstruction that only an Explosive Dart and a Sticky Bomb can demolish. Bentley is the only character capable of reaching this treasure.