im properly not the first but spot this easter egg
The M6 Personal Defense Weapon System is the standard sidearm family of the UNSC. The M6 family is designed primarily for ruggedness and reliability. Certain models have been up-sized to be used by Spartans in Mjolnir armor. Even though the Spartan issue pistols are larger than the standard-issue variants (~117%) they can still share magazines.
[Edited on 07.18.2009 1:19 PM PDT]