There's a meta question here of the feedback loop.

If I pay via coins / credit card the parking meter will tell me "Okay, you have XY minutes left." If I pay via the app, does the meter update as well? If I pay via the scam app... presumably there is no feedback loop, though people may not realize this.

As a second order effect, wouldn't it make sense to investigate the domain and find the owners? Assuming they are paying some other party to put these stickers up the owners of the domain are the real problem. Telling residents to educate each other feels similar to the trope of you are a "victim of identity theft" when Equifax loses your personal details.