I'm reasonably certain that it was Bill Bryson who, in one of his books about the idiosyncracies of the English, mentioned the Yorkshire wave. His description of this regional phenomenon was a raising, by a driver, of the index finger on his right hand while keeping both hands on the wheel. This gesture could be an acknowledgement of a courtesy or it could a form of greeting addressed to another driver or a pedestian known to our Yorkshire driver. The response to such a greeting varies. It might be a straightforward repetition of the gesture (from another driver) or a pedestrian might simply nod - but only gently. Except for a Yorkshire tyke used to spotting the gesture, it would often be missed and many a driver has left the county fuming at the bad manners of its drivers.
(Actually, I made that last bit up.)
The Yorkshire wave has now been adopted almost universally, albeit in a modified form. One solitary finger might be in order for those dour northerners but we soft southerners will raise not just one but all four fingers while gripping the steering wheel with the thumb. We might, on occasion, be sufficiently reckless to raise the whole hand,
There is one thing I have noticed - and this is where I display my chauvinistic streak. Women drivers have a tendency to do one of two things, both of which are easily missed by the other driver for whom the gesture is intended. They might raise the hand when too far away for it to be easily seen so that when the courteous driver expects to see an acknowledgement, it has come and gone. Or the woman driver is so terrified of losing control of her vehicle (that's the only reason I can think of) that the gesture is over far too quickly and, again, the other driver misses it.
Of course, neither the Yorkshire wave nor its southern equivalent are of the slightest use after dark - or, come to that, when driving behind tinted glass - as neither can be seen. Some drivers revert to flashing their headlights, others (I am giving them the benefit of the doubt) continue to wave. Me, I do the opposite of flashing: I switch my headlights off for a split second. I wouldn't want anyone to accuse me of being a flasher.
Earlier this year, I realised that the Roman Camp would make an excellent spot at which to photograph the sunset.