N/S = Near Side ,i.e. the side nearest the kerb (or farthest away from where you are sitting!)
O/S = Off Side, i.e. the same side as the steering wheel
James
As the OP is in the USA I would use left and right. It would seem we are pretty much the only entity that uses N/S and O/S and as they drive on the "wrong" side of the road across the pond...
