here's some signs u can use to communicate to ur teammates (and enemies as well):
hump (squat multiple times on an enemy) = "i own this guy, and therefor have the right to squat on his dead corpse."
whack (melee a dead corpse) = "i own this guy, and therefore have the right to whack his dead corpse."
reloading (press reload button) = "i'm reloading my weapon right now, feel free to shoot the enemy in front of us"
stray bullet (kill your teammate's dying prey) = "i am a kill-stealer. i like to get kills in a dishonorable fashion."
chicken flap (jump up while tapping the squat button) = "i suck so i'm gonna do this idiotic move."
friendly fire (shoot your own teammate) = multiple shots: "i suck and i can't kill the enemy, so i'll kill you instead." single shot: "hey dude, i need your attention. but i wuznt trying to KILL you, hence the single shot. don't be angry."
question mark (draw a question mark on the wall with your gun) = "where is the love? people runnin people dying, people hurt and people cryin. father father father help us. need some guidance from above."
the passive stance (enemies don't shoot back at you when you shoot them, instead try to get the ghost into trees or up the walls) = "hey, this room is for tricks only, u bastard"
that's all i can think of right now. not sure if this can help with team stratemagizing or anything.