This is what I do to communicate something without typing anything.
looking up and down like you are nodding your head yes tells a person I am ready to go. Indicating that I have enough ammunition, health and armor to make a run or attack on a position, or say yes to a request
Looking from side to side says no I am not ready, or says no to a request.
To ask someone to follow you and if they are equipped to go on a run, approach him face to face and strafe left and right. Like you are getting in their face. Then they should reply yes or no, or begin to follow you.
To tell someone to go a certain way shoot over their head from in front of them, then shoot in the direction you would like them to go. do this until the person nods yes or or no, or heads to where you want them to go.
To tell everyone to hold a position duck repeatedly. To tell someone to hold a position you can duck and shoot over their head then at the spot you want them too cover, or duck and shoot over their head from the spot you want them to hold. Do this until they go to the position or nod yes or no.
Shoot at someone's feet to tell them you are going to follow them or wait for them to take a position before you pick one. This also prompts the person to tell you where they would like you to go.
Shooting at your own feet tells people you need health. If someone does this near a health or HEV machine they are asking for cover while they charge up.
Shooting strait up in the air tells people you need ammo. Assume they need ammo for the weapon they are currently holding. This also means swinging the crowbar while looking strait up. Since it isn't to wise to waste ammo while telling people you need it.
You will probably have to repeat an action before a person recognizes it, more so as lag goes up, and less so as you become more experienced.
Also if friendly Fire is on don't shoot people when signaling them keep it safely high for over the head and low for shooting at the feet. If friendly Fire is off then shoot them right in the head unless they get mad cause they keep thinking another team is shooting them. Same for the feet.
If you use these signals you will quickly learn to notice when people are communicating with you and will understand what they are saying easily this allows you to communicate with almost no break in your game play. As well as keeping you moving to make you a harder target.