I think its getting more common in the UK. Where I live we have allocated parking spaces and we were given stickers that are a real pain to remove to stick on cars that park in our parking spaces. I've also seen them available to people who are registered disabled so that they can stick them on cars illegal parked in disabled bays in shopping centre car parks etc.
Personally I'm all for the ones illegally parked in disabled bays, there is no excuse for that as some people genuinely need them, especially during busy hours. In my own experience when someone has parked in my space I just block them in. It doesnt take them long to call my intercom and I'll just say I'm in the shower and I'll be down in a bit to move it, 30mins of waiting around usually ensures they dont make that mistake again....in fairness to the OP its clearly signed where I live that the parking spaces are private.
As for how to remove them, I have no idea other than the ones suggested...the pack that I was given contained no removal instructions :!: