One method for dealing with illegal parking that I employed a while back to great effect was to have a Windscreen notice, but also to keep a record of the times I had placed a notice on each car (by plate no.) and making sure each new notice had a written record of all previous notice issuances. I had a space on the notice with space for 5 notice records (maybe generous I know, but I didn’t really want the hassle of escalating cases too often) with the implication that, after the 5th notice, the matter would be escalated to a Notice to Comply with the potential for fines. I very rarely had to give out more than two or three notices on any one car. It only took a little more effort than simply having a wad of Notices ready to deploy, but the implication that the offenders were being tracked was quite effective.