HI BEN

On the Halo 2 level "Regret", there is an easter egg with the words "HI BEN" written on the ceiling.

How to find it
You will need
 * A sniper or beam rifle
 * The Sputnic skull

Start the level Regret and proceed till you beat the drones and elites go to the outside and to your right you will see a temple with no bridge. Grenade jump there and go to the room to your right. Activate your flashlight and go to a left corner and snipe and you will see it.