A headlight flash from an oncoming vehicle with the driver holding a log sheet/book in the windscreen was a signal for you to pull in and update or make out a log sheet or make an entry in your log book.
Got me out of the s*** many a time.Sometimes I never made a entry in my log book until halfway through my shift.Log sheets were the best idea,not numbered so you could tear one up and make out another so you could get home or to some favourite digs.
Great days.

Chris.

Four truckers arrived at a crossroads together; one flashed; they all went and collided in the middle. Turned out the guy who flashed was simply attracting the attention of his pal who was walking along the pavement. (Based on a true story)