We have the buttons, on the steering wheel to flash the, headlights and tailights.
We always try to use them, with trucks and RVs. Car operators don't seem to care much.
Our coaches with a toad and Pick ups with fifth wheels and many trailers are nearly or as long as semis. It is good to know we have cleared someone we passed.
Of course we have the rear camera on all the time too but.....
The more you drive the easier it is to judge if the tail end has cleared the vehicle you are passing but Women and some men don't have as good depth perception. Don't get offended Ladies it is just facts of the human makeup.