Not sure what the solution is. Reducing capacity to push a policy (HOV lanes, EV charging spots, handicapped / pregnant mom parking spots) is tricky.
Keying cars parked improperly (love the Cayenne double-parked in EV spots in the video) is really just going to generate animosity. Stickering their cars, while funny, could also get someone really worked up. Piss off someone who doesn't think twice of parking in a reserved spot, and you'll eventually get someone who vandalizes the EVSE. Vandalize enough EVSEs and the companies won't replace them.
Tucking a card under a wiper requesting that the spots be reserved for EVs is relatively inoffensive. I would bet that most offenders are either inattentive or suspect the sites are inoperative or not being used by anyone .. and a polite note could dissuade a number of them from future offenses.
Placing chargers in less desirable spots -- or possibly unconventional parking spots -- might work.
Placing chargers between two or four parking spots would reduce the possibility that all accessible spots will fill.
Citing could work - not sure about the private property thing. How does that work for handicapped spots? EVSE with proximity detector could automate the notification process. But see also working people up, above. Obviously this works better with parking that's already metered and has a citing force patrolling the site.