[Coley]

Whenever I see someone pull into a handicapped spot I always check to see if they have the card if I'm near by.
If they don't, I simply remind them directly that they are in a handicapped spot...no need to start with confrontation, they might have not seen the sign...noting that a lot of them fade out pretty badly.
If someone does not take the comment well....I simply take a pic of them and their car (w/ license plate showing) parked there, which is submissible for ticketing.

That said, I would guess that about 1/2 the people that park in the space with cards...are probably not the person who is handicapped.
Often people borrow or use their parents or spouses cards for the parking advantage and this is a lot more uncommon that people admit to...certainly if they are doing it.
I've seen more than my share of people bounce out of the drivers seat of a 'handicapped' car and quickly head into the store....with no visible signs of disability at all.

C.