Halo4ARG posted details of the glyph puzzle which you can enter on Halo Waypoint. Once you've entered the code, you'll have to take on the task of completing the entire "Halo 4" campaign on Legendary difficulty either in co-op or solo to earn 50,000 experience points plus the LASO Emblem. Oh, did we mention you had complete the game with all 13 skulls turned on? Yeah, there's that too.
While some skulls like Grunt Birthday Party and IWHBYD are relatively harmless, others like Catch send enemies on a grenade throwing spree. And, of course, Cloud disables your motion sensors while Blind takes away the rest of your HUD.
Most of the glyph puzzles have been solved to this point and they unlock either XP or Raider armor or both. You can check out all of glyphs found so far over at Halo4ARG.