Traffic Cone

Halo 3
In Halo 3 it is on many human based maps, such as The Pit and Foundry (Heroic Map pack). These cones are usually found around fusion coils. If the fusion coils are shot, or a grenade is thrown at them or they are stuck with a plasma grenade/spike grenade, the traffic cone will shoot across the map at great speed. It is possible to be splattered by a traffic cone.

Halo 2
In Halo 2 the traffic cones were a triangle with an exclamation point on them. There was a Scarab Gun in Halo 2 that floated over a traffic cone.

Trivia

 * The first person to get killed by a traffic cone in Halo 3 got awarded Recon. (Please note that Bungie employees do not appreciate getting constant emails about being cone-splattered.)
 * If you get a splatter kill with a hornet and look on Bungie.net it says you were killed by a traffic cone.
 * By setting down a flag in CTF next to cones and you throw a grenade the flag will fly across the map.
 * If you get a kill/killed by a traffic cone, on your Bungie.net profile it will say under classified: "I'm calling my lawyer!"