In the levels The Armory and Cairo Station in Halo 2, the player can find a hidden message Easter egg. The easter egg can also be found on the DLC map Elongation, which utilises several assets from Cairo Station.
On almost every control panel in the armory as well as multiple control panels throughout the rest of Cairo Station there is a screen with the message:
CODED MESSAGE: WU 1120 REJECTED BY ADMINISTRATOR REV. PAIN MAY CONTAIN HARMFUL CONTENT. RESULTANT PSYCHOLOGICAL DAMAGE ACTION: CENSORED
"Rev. Pain" is the player name for one of Halo's creators from Bungie. The "Wu" may refer to Louis Wu, the alias of Claude Errera, the admin of halo.bungie.org. Alternatively, "Wu" may be a reference to Michael Wu, a senior employee at Bungie who worked as a single-player environment artist for Halo 2; he may have been personally responsible for the Easter egg and included his own name.[1]
The Easter Egg does not appear in the Halo 2: Anniversary remastered graphics mode.
Gallery
The message on Elongation.
Sources