The 1M should be the “M”, the M2 should be called the “MM”, the M3 “MMM”, the M4 obviously would be the “MMMM”, and the M5 should be “MMMMM”
The M6? Just cover the fucking thing in M’s. Don’t even bother painting it, just cover it in M badges/stickers.
Also, dibs on the license plate “U WOT” if BMW ever makes an M8 and I can afford it.