My Mom has used a placard for years. She was one of the 'early adopters' around here - when the whole system came in. Nobody really got the message that these were reserved stalls. So, she had a wad of pre-typed notes in her purse all the time. If she saw a vehicle parked in the handicapped stall without a placard, she put a note under the wiper that said something to the effect of... if you have a placard, please use it because one of these days they will start handing out tickets, and if you need to park here and don't have a placard, here is where you go to get one, and... if you are anyone else, please consider that use of these parking stalls is reserved and the ticket police are going to start enforcing.
Well... more than once at the grocery store, someone saw her put the note under their windshield, and tracked her down in the store. Now... it was OBVIOUS that Mom needed the placard - never any problems on that front. 9 out of 10 who tracked her down... had come to say either "thanks for the info" or "thanks for reminding me to use my card". Only ONE got mad. I think she had to threaten him with one of her gutter canes before Dad showed up.
My brother used to work in construction, and always had his nail-belt on (this is back in the days before power nailers!), and if HE saw anyone without a placard parked in those stalls, he'd "accidentally" spill a few nails. They would get far enough to vacate the stall before they knew they had a problem, and never figured out where the nail in the tire came from.
In reality? ALL of us would do better if we parked as far AWAY from the mall as possible, and used that as an excuse for a stroll. Note: how far away is "possible" depends on whether you are disabled or not, so of course... all the close ones would be available for the new-Moms and the old folks and the rest of us who can't navigate so far.