The Glorious Flag is treasure that can be obtained in Sly Cooper: Age of Thieves in the episode Coopers of the Caribbean. It is worth 248 coins and the time needed to reach the safehouse is fifteen seconds.
"The glorious flag of the glorious pirate ship, the Ruby Harlequin, was once owned by the formerly glorious "Laughing Captain", H. Y. Ena. Now, the glorious glory of this flag can now be displayed in your glorious safehouse. Glorious, is it not?"
It is located near the entrance the ship graveyard, just north of the first broken mast. Sly needs the Mascot Costume to access this treasure.