Sid Graffiti Achievement in Halo: The Master Chief Collection

Load up a Custom Game on Coagulation and head towards the main cave where the Overshield/Active Camouflage spawns. Once inside, walk towards the arched frame that overlooks a small pond. On the left side of this arch, you will see a faint message of “Not Sid Was Here Not” etched into the rocks. The writing may be a little hard to read, so try looking at it from different angles until the achievement unlocks.