There is always a few in any group that gives the rest a bad reputation. Since we are bigger a few can make us look really bad. Lack of courtesy is not unique to RVing. I do not need a sign to remind me to pull over if I am holding up traffic. Unfortunately it's usually a slow car in front of me that's causing the problem but I'll still pull over so that the cars behind me stand a better chance of passing it. If there is a passing lane coming up I'll lay back and get a running start on it so that I can pass quickly and not tie up the passing lane.
It's lack of courtesy and you can't fix stupid.