I almost always do. Say when you're just walking by someone in a parking lot or any other encounter?
The reactions always interest me so.
Some ignore me.

Some very uncomfortably and sheepishly mutter Hi, and get away from me as quickly as they possibly can.
Some have an inquisitive look as in " do I know her?"
Some come right out and ask in various ways " do I know you"?
Some strike up conversations.