I live in the US and was a kid in the 80s. I have never, then or now, seen this done. As a kid, if I did see something like that, I probably would have thought it was incredibly dorky.
But perhaps it is smart. Because what I did see was kids taking out their removables (retainers, bionators, frankels, etc) and setting them on their lunch tray while they ate. And then throwing them away by accident. I wonder if that is still a problem today?