Dogtrousers
Kilometre nibbler
When I was learning to drive years ago, I let a bus out, as the driver pulled away, he stuck his arm out of teh window and gave me a big thumbs up. Does that trump a flash?
I recall a public info poster informing us that we should be good citizens and let the bus out, depicting a bus with a thumbs up hand extended by the driver. This would be a long time ago. Decades.Never had a flash. I usually get a thumbs up out of the window.
Rear light flashing, from buses and cars, is pretty common these days but I think it is a (relatively) recent innovation with the advent of cars having a hazard lights button.