RB is red/brown, RD is red, BN is brown, C is cameo, U is ultra cameo, and based on M having no big numbers, I assume it means it's a minger.
This really is a triumph of marketing over gullibility. How do they scientifically determine what constitutes cameo or deep cameo? It's all in the eyes of the beholder, or maybe a sop to the submitter. After all, this got an ultra cameo rating, conveniently ignoring the repair. Before and after pictures. In the slab - £21K ($30K) hammer + juice to the US dealer who bought it, and something on top of that for the client.