"Smiling is a universal human practice, although readiness to smile at strangers varies according to culture. In Australia, where being open and friendly to strangers is not unusual, the city of Port Phillip, an area covering some of the bayside suburbs of Melbourne, has been using volunteers to find out how often people smile at those who pass them in the street. It then put up signs that look like speed limits, but tell pedestrians that they are in, for example, a “10 Smiles Per Hour Zone.”"

it's really nice when you smile at someone as you pass by, and they smile back.
i smiled/said hello to a man on a run with his little child on her bike, and all i got was silence and a glare.
smiling is nice.