The Diamond Saber is treasure that can be obtained in the episode Coopers of the Caribbean in Sly Cooper: Age of Thieves. It is worth 247 coins and the allotted time needed to reach the safehouse is forty-one seconds.
"Carmelita's English ancestor, Commodore Gabriel Fox, had intended on his descendants inheriting the saber, and with the diamond on the hand-guard, it was only a matter of time until it was seemingly lost forever, mainly due to thieves. Thankfully, it has since been found, and Carmelita will cherish it for the rest of her life. Funny how things work out."
It is located on top of the governor's home, directly above the front entrance. Only Carmelita can obtain this treasure.