DMM 2003

The Hidden message in Timberland can be seen on the Halo PC multiplayer map, Timberland.

How to do it
In order to get it, grab a Ghost and go to the hill just on the left of blue base. Drive to the top of blue base (may take a few tries), get out of the Ghost and land on top of blue base, and you should be able to run up the rest of the hill. Run left towards the corner of the map. Behind some trees is a secret message. Written in black scorch marks next to the corner of the map says DMM 2003.

Trivia

 * The DMM stands for David M. Mertz, a multiplayer map designer for Halo PC and the 2003 is the year that Halo PC came out.
 * It is unknown why Timberland was chosen as the map for this easter egg.

Related Links

 * Halo PC
 * David M. Mertz