Interesting topic.

I've noticed the further south in the UK you go, the less you're acknowledged.

I always nod or tip my head at other bikes, except when riding in Europe where I'll follow their usual wave with the clutch hand. I don't flash as it can be misinterpreted and as UK traffic laws stand, if it leads to an accident, you're at fault. I'll signal with my palm flat and down with an up-down movement to warn oncoming bikers of an accident or police presence (far more common in mainland Europe) but I'll always make a point of acknowledging police motorcyclists. Goes without saying that I pull over for anyone that looks like they need help.

Also pull the clutch and wave with throttle hand to horse riders and you'll nearly always get a wave and a smile back. I also make sure that I give a thumbs up to car drivers who move over to let me pass, particularly if filtering. It's just a little bit of recognition of their good driving and observation and hopefully they'll keep doing it.

I tend not to nod or wave so much if I'm somewhere where there's loads of bikes, such as a popular meeting place, race meeting, etc, but thats just common sense. I don't usually wave at anything with L-plates unless I get a nod first, well.. maybe I'll wave at 125's if I'm having a good day but that's normal I think.