^ That brings up a different point. We never really saw enlisted rank insignia in TNG (at least I don't reall ever seeing it), so how would determine rank among the enlisted personnel? Or just simply refer to them as "Crewman"?
Well O'Brien is a "chief" i'm assuming "chief petty officer"
There would probably be sergeants etc among the NCO's, but I think officers generally refer to them all as "crewman" because of the divide in rank.
I think anyways