Instructions
Start a game of "Uncharted: Drake's Fortune."
Press "Start" to pause the game. You can do this at any time during play.
Choose "Bonuses" from the Pause menu. It is the second option on the page.
Select "Rewards" from the Bonuses menu. It is the last option on the page.
Pick "Costume-Select - Heroes" from the Rewards menu. It is the First option on this page.
Press Left, Right, Down, Up, Triangle, R1, L1, Square. If you enter the code correctly you'll hear a chime, and the option "Baseball Shirt Drake" will be unlocked. It may take a couple tries to enter the code correctly. If this is the case, don't worry. You don't have to exit the menu and return to try again. Simply re-enter the code.
Highlight "Baseball Shirt Drake" and press "X" to toggle this costume option on or off. Press "Start" to resume the game. Drake will have on a different shirt that resembles a baseball jersey. Nothing else in the game will be any different.