Marathon Cross references
During the first level of Halo sometimes a marine will say "Look a Mark-Five". An apparent reference to your MJOLNIR armor.
In Marathon Leela mentions Mark IV soldiers (Spartan I's?):
"There is surprisingly good news planetside: nine military Mjolnir Mark IV cyborgs were covertly living among the colonists, and acting together they were able to single-handedly turn back the latter stages of the Pfhor assault. Casualties on the colony were nowhere near as high as those we experienced here on the Marathon."