Agreed US crews and non-US crews are very different in approach to seat belt sign usage. One example:

I flew Icelandair DEN-KEF years ago, and the seatbelt sign came on immediately after door close. Before we pushed (plane still stationary) a passenger stood up and an FA immediately intercepted, said the seat belt sign is on, you better sit down. And they did. The moment we hit 10,000 (not long when climbing out of DEN) the seatbelt sign went off. It came on mid flight for about 10 minutes of turbulence, and was off until a few minutes before landing then stayed on until the gate. And during those 10 minutes mid-flight people immediately returned to their seats.

Seems like UA and the other US airlines now *always* hold the seatbelt sign on until top of climb (why?!), then turn it off, then FAs start their service - meaning no trip to the lab if in Y on a narrow body and you are seated near the front. Then, the light magically comes back on soon as the FAs finish their service. So, people just get up whenever they please because the 'always on' seatbelt sign has become meaningless.

So, is the seatbelt sign about safety? Or is it about risk management for the airlines - so they can always say "seatbelt sign was on, it's your own fault for ..." How did we get to this point? Serious question.