I should have added the most important thing....pay attention (which applies anywhere, of course) without looking like you are paying attention to anyone or anything specifically. If you are aware of what's going on around you, it's much easier to spot and avoid any potential trouble....but you don't want to appear snoopy. Am I saying this in a somewhat understandable manner?
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"Let us hope our weapons are never needed --but do not forget what the common people knew when they demanded the Bill of Rights: An armed citizenry is the first defense, the best defense, and the final defense against tyranny. If guns are outlawed, only the government will have guns. Only the police, the secret police, the military, the hired servants of our rulers. Only the government -- and a few outlaws. I intend to be among the outlaws" - Edward Abbey