How about those black on white signs that said "Quiet Please," "Keep Moving," and "Please Find Your Seats." Like clockwork, those signs would get raised above everyone's heads by the attendants. The Find Your Seats sign would be used during the 10 minute musical interlude just before the morning session would begin and also right after lunch just before the afternoon session would begin.
The Keep Moving sign would be used by roving attendants - the ones that would walk circles around the corridors. This was to encourage herding everyone to keep walking and not to clog up the corridor by talking with your friends. These signs typically were only seen during the lunch break.
And of course the Quiet Please sign was also for the roving attendants circling the corridors. This sign was to used to bring about guilt for speaking too loudly in the corridor when walking with a friend. You would only see these signs during the assembly parts.