Upon double tapping on a room, you'll get a clipboard(i think) icon on your lower left side, clicking on this open a assign menu for the given room giving information on how many is working there, how many the max limit is and character names and specials.
Ah, thanks, Superdeluxe -- that's the kind of tip I was looking for. I wasn't aware of the +/- thing. That's easier than clicking on a room and then clicking on the clipboard.