Bulletin board
From Halopedia, the Halo wiki
On the first and last of the Halo: Combat Evolved levels, a bulletin board can be found just outside the bridge of the Pillar of Autumn. Some of the seven messages look plausible, some are just silly, while others are hidden Easter Eggs. There are actually more bulletin boards on the Pillar of Autumn, one being found on the mission, The Maw, there is a shattered board right through the cafeteria alongside two medical packs and an empty shotgun.
One says: "Missing: Calico Cat: Answers to Jonesy" This is a reference to Alien and Aliens, two movies that Halo draws inspiration from, to include the banter of a Marine soldier. Jonesy was a Calico cat in the series and, along with Ripley, was the sole survivor of the first movie.
There is a picture of Earth from the Moon with the caption "Fight for her" on it. This is likely propaganda within the UNSC. It also shows Africa, and may be a reference or foreshadowing to where the Ark's portal is hidden.
There is also a note reading:
For Sale:
Pentium XI 33 GF
Chicago Office
Colony Ship
*7 Speed Manual (a another 7 reference) transmission. (all of that goes with the colony ship)
Hyde Park Condo
Integrity
This is a reference to Bungie being bought by Microsoft. It mentions the location of Bungie's old office, as well as referencing a stage in Marathon, entitled Colony Ship for Sale: Cheap.
There is a sign that says: "Marines keep it clean! Clean your area, toss your filth, put away your trash." This may or may not be linked to the latest teaser by Bungie entitled "KEEP IT CLEAN."
Another says: "Duty roster Pillar Of Autumn" with some illegible writing which is supposedly the duty roster.
One says: "Marines scooters are for squirts, no scooters on deck."
Another reads: "Attention marines, callbacks for South Pacific" and the rest is cut off by a keyboardish item. It is likely that this is a reference to the musical, South Pacific.
