Abbreviations on Champagne bottles 

RM, NM, CM, MA, ...

En voici la liste :
RM : Grower-Manipulant
NM : Trading-Manipulant
RC : Grower-Cooperator
CM : Cooperative of Manipulation
MA : Manufacturer's Brand
SR : Company of Cultivators
 
RM Does not mean it's a better Champagne, but that it's just a Harvest Champagne. The big brands (NM) also produce interesting, typed cuvées of always equal quality.