I determined that the 10 forerunner icons on the waypoint image fit together in order like a puzzle. Start with the the two icons with flat sides on their “pieces” and work your way in.
It will apparently work once you’ve achieved some prerequisite, which I have not achieved just yet. At least that is the message it gives me when I enter it, states I haven’t met the requirements.
Yup did exactly the same, dont know the req so I hit up google and got here 
Have either one of you beat the new campaign fully? That might be the pre-req?
I heard somewhere that the requirements have something to do with spartan ops. I think it’s complete the 1st mission.
I found 2 forerunner code pictures on waypoint on the 360, the first was on the main dash and the second you had to go into games and then halo 4 and its the 13th on the list but I can’t decipher it, it show’s me 10 symbols, each with a picture next to it, four have the pictures of the different difficulty settings, 3 have weapon pictures (A battle rifle, Magnum and Rocket launcher) and the other 3 have enemy’s next to them (A grunt, an Elite and a Hunter) I have no idea what it means but I’ll keep trying to figure it out.
beat spartan ops to unlock that code…its for raider sholder pads or at least thats what it unlocked for me…but im lost as how to enter the second one 
Where do I get access to the code? I found all the terminals but is there more?
I think this thread is relevant.
https://forums.halowaypoint.com/yaf_postst130119_CLASSIFIED-Raider-Code-Found.aspx