If anyone on a scooter waved to me, I would return it, no question.
I find that most people who ride scooters do it for convenience (I say most, certainly not all). It’s a way to get around town quickly, and they don’t have to worry about locations that aren’t near the subway, or the bus schedule. I see nothing wrong with that, but that’s why I say that a number of scooter riders aren’t part of (and don’t want to be part of) the motorcycle community.
One interesting thing that I’ve found is that when the weather is gross (cold and rainy), I still see scooters out and about even if I don’t see any motorcycles. Those are the kind of scooter riders who I’ll wave to without a problem. It’s impossible to identify them when the weather is nice though, which is a shame.