it’s always very difficult for posh people to know where to park their cars.
in theory, even today, the very wealthy are legally entitled to park their cars wherever they like. but of course this aggrevates the working classes who end up with nowhere to park their horse and carts.
Sometimes people have become so annoyed they have literally spoken to each other about it.
Obviously something had to be done. which is why some parking spaces have been reserved for specific types of vehicle. like this BMW.
Unfortunately the sign seems to have been written by someone of a lesser education, with the result that the M is missing.