I make eye contact smile, and comment on the weather or some such foolishness, while I hold the door, and give the wave on thru motion with my hand.. 99 % of the time it will invoke some kinda response, and usually a "thanks"..
kinda stumbled into it.. if I just stopped and held the door.. most times nothing was said.. so.. (ya know me Dave).. the smile and the big yap.. gets 'em motivated..
But Slip is right, somewhere along the line.. most manners and such.. have evaporated.. meybe it's society.. people don't trust nobody anymore, and worry that the next guy is a hatchet murderer, or the like.. kinda sad...