Flying AA as mere SLF a few years ago, I seemed to go through a whole period of the flight crew including in their basic announcement something like:
"Folks, I'm going to turn the seatbelt sign off so that you can move about the cabin if you need to. But when you're back sitting in your seat I really do recommend that you do like we pilots always do here up front - have that belt fastened whether the sign is on or not."
Certainly got my attention - and to this day I always have the belt fastened unless I'm actually standing up. And I've - successfully - shared the story with seatmates too, over the years.
Haven;t heard such an announcement for many years, though.
AGB