Face in Halo
From Halopedia, the Halo wiki
This easter egg is in Halo 2 on the multiplayer Containment (Level), where a face can be seen in the Halo ring. The face is thought to be Bungie team member Frank O'Connor or Chris Carney.
It can be found by standing near the red team's base where the turret is, then zooming in with a sniper rifle at the ring (Even though the Sniper Rifle Scope isn't required, it may be seen through regular zoom).