The word spartan Ops: In Halo 3 campaign, Crows Nest. found on a wall, or on the side of a green box (cant remember where but i remmeber seeing it).
The purple lights in the trees. in the map abandon can also be seen in halo 3 campaign
Mission Ark after the 1st wave of grunts you walk through a small cave tunnel which is lit up by some small purple lights.
this is just something i found while playing halo 3 campaign.
Drone AA in halo 4 also from missions ark and halo. which you can use.