When Percy, Annabeth, and Grover first meet up with Luke right before they leave the Demi God camp (when he gives Percy the winged shoes), he's playing Modern Warfare 2, and you see him playing with a PS3 controller, but if you look at one of the screens, where it's on a pause screen, you can see the green A button from the X-Box 360 controller (from when it tells you to press a to select)