The label is often called by the name 'M'. The name Maurizio is after the main artist releasing here.
The releases do not really have catalog numbers. For M-4 to M-7 the releases were numbered in their titles, so the catalog numbers are assigned after these titles (as can easily be seen below). The first three releases have their 'catalog numbers' assigned in order of appearance. The original EFA release of the CD didn't feature any catalog number besides the distributor's, as well, 'M-CD' is only given to fit it in with the rest.