Note in Armory

In the level The Armory in Halo 2, the player can find a hidden message with relevance to the Halo fanbase.

Message
On almost every control panel in the armory, there is at least one 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" likely refers to Louis Wu, the alias of Claude Errera, the admin of halo.bungie.org.