Interesting question with no foolproof solution. Sounds like the law abiding citizen will more than likely have to go defensive, taking cover until they can make a decision they are willing to live or possibly die with. Perhaps simply focusing on saving their own butt and that of their family and friends accompanying them which means taking out potential BGs is secondary.... How do we identify ourselves to each other? If bad guys dressed in plain clothes open fire and several armed citizens respond. How do we know who the bad guys and good guys are? I would bet on the guys with assault rifles being the bad guys and concentrate on them. I have thought of this and can’t come up with a way to indicate to others around me that I am a good guy without yelling it out.