This firm produced perfins from 1884 to 1892.
Here is a Melchers Sucesores cover produced in that time:
Used 3 February 1886 from Mazatlan to New York City
"M" perfin on 2 centavos Miguel Hildalgo definitive (1884) - Scott 151
Here are some of the stamps which have "M" perfins:
Melchers Sucesores storefront from a book entitled "Mazatlán in the XIX Century"
Melchers Sucesores factory from same volume.