Why Am I Here? Achievement in Halo: The Master Chief Collection

Load up a Custom Game on Beaver Creek and head towards the perch where the Sniper Rifle spawns. From here, continue past the weapon and jump onto the cliffside ledge. Turn to the left slightly and melee the large rocks here so that they fall off the ledge. Right behind the rocks, you will find faint, etched writing with a signature that reads “Not Sid.” The writing may be a little hard to read, so try looking at it from different angles until the achievement unlocks.