I haven't found the maker either. There are many that aren't listed in databases.
However, always look for alternate possibilities. Many took "artistic" variations for their logos that make sense to them...and years later not for others!
So it is possible the name could be related to:
HMCB (remember, on monograms the center letter could be last name) and the small letter could stand for Brothers. So, just for an example Harold and Milton Conley Brothers could be HCM