u need to get action replay for xbox. This will turn of the hud and allow u to have no weopons so u dont see ur arm. (if u r using xbx live) If ur in campaign get the blind Skull.
Unlockable: Blind Mode
At the beginning of the episode Outskirts, go through the first opening but do not head down the ramp. Instead, jump up onto the flourescent lamps over the doorway. From there, you can jump-crouch-jump onto the sloped roof to the left (jump and hold the crouch button at the peak of the jump to get onto the ledge).
Once on the rooftop, look for a narrow alleyway directly to your left. At the end of the alleyway are some grenades and a skull. Picking up the skull (hold the X button) will unlock blind mode, which removes all traces of your HUD. To get them back, save and quit. Then choose Cairo station, save and quit and then choose the level Outskirts.