In CA, not only do you have a "hanger" but you can obtain plates. I chose the hanger because i use two cars and my MH. When you get the permit, you also get a "registration" that stays in the vehicle. In my case, I copied the permit and put a copy in each vehicle. Never had a problem, although I have been asked if I was aware that the space I was about to park in was handicapped. Here, there is a number on the hanger that LEO can call in to see who is permitted. Doesn't say what the disability is , just who has the permit. When I am in another persons car, I take my permit, but not the "registration".
In my case, I have had THREE hip replacements, Myasthenia Gravis and circulation issues. At the present time, I walk well and don't seem to be having any difficulty getting around. However, I can exit my vehicle, go into a store and suddenly "crash". Getting back to my vehicle can become a chore. So, as previously posted, just because someone looks healthy and hale, doesn't necessarily mean a thing.
As a former LEO, I am very aware of the abuse I see daily with the permits and laud officers for checking permits when they feel it is necessary. I think the fine for abuse is not adequate, although here the hanger is confiscated and a ticket issued. Of course, that affects the legitimate users ability to get around.
I don't mind if someone asks me if I need the permit. I would be offended if they started yelling at me. However, I would take into consideration their ignorance and lack of class for doing so.