Misriah

Misriah is a corporation or government agency that develops weapons for the UNSC. In the Art of Halo book it shows a side view of the M6C Magnum Sidearm and it has Misriah stamped on the side.

Trivia
Misriah is also an organization in the Marathon Universe:

The Rose (Terminal 2)

On January 6, 2345(Earth A.D.), at the United Earth Government Misriah food distribution center, what had begun as a commonplace food riot turned into a massacre. The UEG riot troopers who arrived at the scene had been informed that the rioters were armed. As the UEG troopers approached the scene in their Randal Hovertank, plasma fire began spraying upwards. In a flash decision, the commander of the Hovertank ordered his crew to open fire upon the crowd. It took only five seconds for over five hundred starving Martians to be incinerated.