Most American air crew have no idea what the AIM definition of turbulence is. I have sat in trail of a heavy reporting moderate when all I have felt is a occasional light many times. I have also been a prisoner in the back, unable to use the lav in smooth air. On a short flight across the US it is almost tolerable, but crossing the Pacific it becomes unbearable.
Passengers in the US completely ignore the seat belt sign. The sign is always on!
When I was a Captain flying domestically many years ago I would ask that pax keep their belts fastened at all times, just like we do up front, just like they do in their cars. I would ask them to limit their movement during meal service to appease the Flight Attendants. I did not use the seat belt sign for crowd control.
For passenger safety and comfort I suggest that the seat belt sign should be used only when it is needed.