Children and families on bridges I'll definitely wave to, the last couple of weeks has been pretty busy.
I've stopped tooting the horn, as on the desiros I drive they are very loud even when you try to get the smallest toot and I've had a couple of incidents where it does more harm than good when it comes out real loud and the kids look scared....
When pulling into a platform im stopping at, if children wave I'll try to wave back, even if it's just a acknowledgment via side window, but I'm focused on the red signal on the end of the very tight car stop mark so sometimes there'll be no wave.
I don't respond to random requests, especially the horn/whistle tugging hand action and very rarely to adults waving, though sometimes I guess they are well meaning, it does seem a bit odd. I do however wave to the occasional times I see older men ,normally alone standing on bridges, as I have some belief, without any evidence!, that they may be retired drivers or signallers. Don't know why......