Grand Commendation
The Grand Commendation system, introduced in patch 5.1.0, allows players to boost reputation gains for all characters on their account with certain Pandaria factions.
Each Grand Commendation is bought for a small sum of gold from the corresponding faction quartermaster. It is a heirloom quality item that must be used after purchase to take effect. Simply having a Grand Commendation in one's bag does nothing.
Grand Commendations are unlocked upon reaching revered reputation with the corresponding faction, and once used, double all reputation gains with that faction for all characters on the account, including the character who originally reached revered. This means that they effectively halve the reputation needed to reach exalted, making the climb from revered to exalted a little shorter (effectively 21,000/2 = 10,500 points) than from honored to revered (12,000 points).
Notes
- Since patch 5.2.0, reputations that have the bonus unlocked were indicated with a
icon next to the reputation bar in the reputation tab. In patch 9.0.1 the indicating gold arrow was removed from the UI. Players will need to keep a mental note of if they had unlocked the bonus reputation for a faction as the tooltip for the item will not state if it is already known or not. Purchasing the item and using it when the bonus reputation is already known and give the error message: Already commended by this faction. However, the item is not refundable so it will need to just be deleted.
- Another way to tell if the Grand Commendation has been used is looking for the bonus text in the reputation earned text. The text reads as follows: Reputation with <faction> increased by X. (+Y bonus).
Patch changes
Patch 9.0.1 (2020-10-13): UI visual removed. 
Patch 5.2.0 (2013-03-05): The Reputation panel on the character screen will now let players know which reputations they have purchased and used Grand Commendations for. - Patch 5.1.0 (2012-11-27): Added.