I've had more people stare at me because I look fine. When I first got my handicap placard I was only 42 years old. I was going in the grocery store and some guy walked past me very quickly and yelled at me as he breezed by for parking in a handicapped spot. I was in Ohio at the time and we had plates that we laid on top of the dash. He didn't bother to check but accused me. I couldn't catch up with him but I yelled back for him to call the police on me. Oh, how I wish he did! LOL
Remember, these handicap placards have to be renewed. In Florida it's every six years. If it is in his son's name, DMV will know he is deceased and he can't get it renewed. If he truly isn't handicapped, he won't have use of it for very long and he will have to answer for it one day. So, don't give it another thought. It's not worth the energy.