Chief EG-X
From Halopedia, the Halo wiki
In the human based projectile weapons the Battle Rifle, Assault Rifle, Pistol, Sniper Rifle, and Machine Gun Turret, weapon casings are ejected when bullets are fired. On the base of these cartridges there is writing that says "CHIEF" then "EG-X"; the first word obviously being a reference to John-117 - the origin of the EG-X marking could be either the trademark of the arms manufacturer or the factory it was produced in. As the writing is small it is difficult to read from even a moderate distance, and because in Halo 3 the bullet casings disappear after a short time, it is easiest to see the writing on the casings in Theatre mode, when you are zoomed in (best done when you are detached from the player). This Easter Egg can be viewed in both multiplayer and the campaign whenever Human weapons can be found and used.
