I hate to make reference to a video game for a question. But, in COD: MW2 the Rangers identify each other with the call sign "Texas" and the person should respond "Star." Or maybe was the other way around. Anyways, not important. THe question is if that happened what would we use to identify the friendly soldiers from enemy? Or in any scenario for that matter. WOuld we use a call sign and countersign system? Or is there a different way? Or is it don't trust anyone? Or it just hasn't been established? Because if Thats the case I think it would be a good idea to establish a system to recognize friendlies.