This is something I've actively done something about. Years ago I drove the wheel-trans for a short time. One time I was picking someone up at a Tim Hortons and some dickweed parked his nice red sports car in the handicapped spot by the ramp.
I went in to look for the owner and found him sitting at a table. When I told him he was in a handicap spot and that I needed to park there, he had the nerve to ask if I could wait til he finished his coffee.

My response was , "How much you wanna fuckin' bet I can get your car towed before you finish it." He became quite co-operative and moved his car right away.
Another time I was picking up at a medical centre and some some asswipe parked his Cadillac in the handicap spot. I made extra sure he didn't have a permit before I blocked him in, dropped the ramp and shut off the van to go get my passenger.
As I'm coming out, I notice him standing there waiting. As I walked by, I looked at him and shook my head.
The moron actually had the nerve to ask why I shook my head at him. My response was, "If you have to ask, you're even more fucking ignorant than I thought!"
In both cases the handicap parking was
clearly marked including signage.