You know that little wave rural drivers used to give one another on lonely country backroads?
Sure. Often it wasn't so much a true wave as a cordial palm-on-the-steering-wheel hand flip.
That tradition probably hasn't died out yet. But the one place you are sure to see it upheld is right here in the city.
STA drivers greet each other that way countless times every day.
They cannot all like one another. That's a statistical impossibility. So this must not be a particularly personal acknowledgement. Maybe it's just the code of the road when you see another bus.