Halo: The Master Chief Collection - Halo 2 - HI BEN - Halo 2: Oh, hi! This achievement is fairly easy to unlock.
On the mission Regret (Have the sputnik skull on), right at the start of the mission run outside and head to the right to the destroyed bridge.
Perform a grenade jump across the gap. On the ground floor head to the right into the room and look up and to the left.
Zoom in with the covenant sniper and text should appear on the wall. This has to be done with the covenant sniper.
Shortly after your achievement should pop! Enjoy!