What I do on my 4/4 when i stick a parking ticket in the windscreen with the roof down is I photograph it on the car with my 'phone, so if it has blown away/been pinched I have some proof that I had paid & diplayed. I guess an unscrewable tax disc holder might be the way forward. Of course with the M3W you have no wipers for them to stick the ticket under......the rest of us have 3 wipers for them to choose from.
