MerylStreep
Serendipity
It’s a British thing, much admired around the world ?
It may have started in Britain in the early days of motoring, but it is no longer a specifically British thing.
I live in the South of Denmark, and on both sides of the Danish-German border both motorists and cyclists raise a hand in acknowledgement when another road-user holds back for them, even when they do not have the right of way and are obliged to hold back, and most of us mouth "Mange tak" or "Danke sehr" depending on which country we are in at the time.
Obviously, if it is unsafe to remove a hand from the steering wheel or the handlebars of a bike, one would make do with smiling and nodding.
I use a cargo bike that has hand-brakes only, which is legal, but to me a flipping nusiance, as Danish bikes often have a brake connected to the pedals as well. When you back-pedal you brake. I grew up with that system, and I can assure you that on the steep hills outside and in Flensburg no power on earth would persuade me to remove one of my hands from the brake, as I am certain I need them both. Otherwise, I do acknowledge courtesies with a hand-sign.