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From
1847 to 1894, all US postage
stamps were contracted to private security firms for printing. The printers
identified themselves by imprinting the stamp or stamp margin, a
traditional practice among security printers, as well as a form of
advertisement. Durland
identifies 29 distinct imprints on pre-BEP issues and 15 BEP
imprints.
Each
stamp of the 1847 issue bore the initials of the printer, Rawdon, Wright,
Hatch & Edson included within the outer frame line of the design.
But in 1851, the printing contract for stamp
production was awarded to Toppan, Carpenter, Casilear & Company. In 1857, new
plates were required and the printer’s imprint was added to the
selvage.
Since Casilear had left the firm in 1854, his name was removed from
the imprint on the new plates, the imprint was modified. An even later
version of the company’s imprint, the Jos. R. Carpenter imprint, was
used on Documentary stamps and the 1871-1874 Proprietary stamps.
 
(Image courtesy of Chip
Gliedman)
In 1861, the printing contract was awarded to the
National Bank Note Company. They continued to imprint each plate,
but their imprints appeared in the top and bottom margins, as well as in
the side margins.
The Continental Bank Note Company reprinted the
1857-60 Issue and a small quantity
were prepared as a Special Printing in 1875.
National, Continental and American were consolidated
into the American Bank Note Company in 1878.
In 1894 the BEP took over production of stamps.
A major
category of marginal markings is markings that provide for the
identification of the printing plate. The plates were normally identified by
at least a serial, or plate, number (although the number may have been
trimmed before issuing the panes). More recently, as the types of printing
proliferated and the private printers became more numerous, the
identification of the plates used may or may not be available to the
collector.
Modifications to a plate layout or plate surface treatments were
also occasionally marked. Plate identification includes the
following subcategories of markings:
A.
Producers’ Identity: Markings that identify the printing firm.
B.
Modified Layout Designations: Markings indicating modifications to
a particular plate.
C.
Plate Surface Treatment: Markings indicating that a plate has
undergone some sort of processing.
D.
Plate Number Types: Plate numbers or plate sequence
numbers.
E.
Plate Position: Markings that identify the position of the plate,
either within a set of plates being used simultaneously, or as placed on
the press. | 
