Screaming Virgin doesn't like it rough? (or VA F/A screams during turbulence)

[flyblue]

My understanding of the law is if the seat belt sign is "on", secure the passengers and cabin, then sit down and strap yourself in. Stop passengers from leaving their seats.

Not always. In my company we have the "Turbulence" procedure, and the "Severe Turbulence" procedure. In the first case, we only get the FSB sign on: we must check the pax SB but don't have to take our seats. In the second case we get the FSB plus an announcement from the F/D "CC, turbulence, take your seats and fasten your SB".
In any case, if the situation is bad, we can ask the F/D to upgrade the procedure from T to ST.