BMW has been using a very interesting way to use M and S letters.
BMW’s regular cars (320i, 530i etc) were powered by M engines. Their engine codes were M20B20, M60B30 etc. BMW Motorsport built sportier cars (M3, M5 etc) that were powered by S engines that had engine codes S14B23, S38B36 etc. Currently the M cars still use S engines but the regular cars have shifted to B and N engines.
Motorcycles have more engine in them than cars so maybe it makes mores sense that M motorcycles would be S motorcycles instead? They could of course start using M engine codes for the S motorcycles to distance them from the S engines used in the M cars.
