All those A-roads and M-roads exist. In addition Audi sell an A1 (the longest road in Britain) and there is the BMW M1 from the late seventies/early eighties. And of course the BMW M3.
No R-roads in the UK but they do have them in the Republic of Ireland.
Along those lines, in Wisconsin county roads are given letter designations, like County Road M, and such. They sometimes use double or triple letter designations. I’m sure there’s a County Road TT somewhere in Wisconsin (because I remember finding TT funny when I was a kid) on which you can drive an Audi TT.