This firm produced perfins on stamps issued between 1915 -1917.
Here are some of the stamps which have M/&co perfins:
Edificio Robins, circa 1920, home of Frank Robins Co. and Monroe & Company.
From a text in Spanish: "It (this building) has six floors that were solidly built, in stone and abundance of marble. The wide and numerous window openings ensure effective ventilation and give abundant light throughout the interior. The ground floor consists of a lounge for exhibition of fine furniture for desks, art objects, phonographs, pianos, cars and thousands of other objects that make up the business line of the Frank Robins Company. At the back of this room, a wide marble staircase leads to the second floor occupied by the offices of the company. On Havana Street, the building has the necessary elevators and stairs for the upper floors, distributed in mercantile offices, which are occupied by valuable foreign companies and offices, among them, that of the Naval Attaché of the United States."