Surpmil is right. The B is a hard 'blue-ish' coating to enhance the light transmission and is said to eliminate (but it doesn't.....?) light scatter. The trouble is that after the average civilian shooter has set about cleaning his lenses - going round and round in ever decreasing circles until he hits the middle - with length of old grime encrusted shirt tail from the bottom of his shooting box, it just removes the coating. If telescopes had been roughly cleaned by the snipers and the coating was partially removed, then we'd remove it all with a slightly abrasive rouge on the basis that the effect was still working (?) along the inner optical system of the telescope. The OG end was the most important because if the coating on the outer convex side of that lens was polished away, when the scope was focussed against the light screen, you'd get a slight 'starry' effect but I digress
The red W is a two edged sign. It indicates on a Mk2W, a Mk2/1 and a 3 that a) the telescope is fitted with waterproof drums* and b) that the telescope is in fact waterproof according to the tests in the depression cupboard. However, that REALLY indicates shower proof - as in the rain in temperate climes and NOT a monsoon in Malaya or as deck cargo on a submarine!
* The W drums are those with a rubber/neoprene/fibre 'O' ring at the base of the thumbscrew, between the index plate and the clicker plate. The Mk2.
I hope that has clarified the point