Came back recently with SIA from Singapore to Heathrow and twice the seatbelt sign was switched on for chop for about 30mins.On each occasion after 5 mins the cabin crew lost interest rapidly followed by the pax,and everyone was moving around with the plane bouncing along,in moderate turbulence.
On the other side of the fence when I was working in ATC in Hong Kong,we had a China Southern who encountered severe CAT over Macau inbound to CLK.However the pilot said absolutely nothing about it either to Radar or Tower,and the first anyone knew was when they opened the door and out spewed numerous injured pax.
I just keep the belt fastened tight all the time especially on Far East airlines.Some don't give a toss even if you do hit the ceiling.