For those of you who don't know, this is the multiplayer map "The Pit" from Halo 3. K2 is a legal herbal smoking blend marketed as being all natural, though it allegedly contains synthetic cannabinoids, which mimic the effects of Marijuana. It is a product similar to Spice.
highly doubt thats on purpose, but i cant say the same for alot of the max ammo in modern warfare 2, which is 420 lol
K2 is also a snowboard company, they made bmx bikes at one point to I think. So no, it's not a subliminal message for some legal high. It's not even subliminal period actually, subliminal implies that it's something that you can't really pickup with the naked eye but your unconscious mind does, this is right out in the open.