I prefer to maintain a bland nonspecific sort of pleasant expression in public, with the emphasis on bland. Encouraging approach from strangers is not what I'm interested in doing, but neither do I want to frighten passing children and little old ladies with some sort of ogre-like demeanor. Communication among humans is after all mostly non-verbal.
Think about who you are communicating with and what you are saying. For instance, take a look at
http://www.teddytactical.com/archive...3_StudyDay.htm . "Normal" people are not likely to be a problem, but predators are a different kettle of fish.
'Social violence' must be considered also as it's likely to be more commonly encountered in ordinary life than predatory violence. I'd suggest getting a copy of Rory Miller's book
Meditations on Violence for a discussion of lots of relevant material - see
http://www.amazon.com/dp/1594391181?...t1_markup.html