Bulletin board

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 messages look plausible, some are just silly, others are hidden Easter Eggs.

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

*3 Speed Manual

*Transmission

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 are other things too. Some you can read, others you cannot. Also you can see the words "Marines Keep it Clean" and "Scooters are for Squirts, No Scooters on Deck". Another says "Attention Marines callbacks for South Pacific...". The bottom of the poster is cut off by the keyboard.

Trivia

 * There are actually more bulletin boards on the Pillar of Autumn.
 * On the mission, The Maw, there is a shattered board on level one right through the cafeteria were you find two medical packs and an empty shotgun.