It's useful to know what a teammate is trying to tell you when talking or using radios isn't feasible. Familiarize yourself with these common Hand Signals, and you'll be a lot less frustrated when your buddy tries to tell you there are two tangos in the bush to your left.
Keep in mind some teams use signals that are unique to their group, so if you see something used that's unfamiliar, it never hurts to ask... just wait until the gunfire dies down.