E - essay, a proposed design
HBg - horizontal broken gum, a horizontal diamond pattern impressed in the gum to prevent curling.
imp, imperf - imperforate
NG - no gum
NM - negative maker's proof, a true printer's proof
p - proof, usually imperforate
pcp - progressive color proof, usually a set of 7 stages showing colors separately and in
combinations, leading up to the complete design.
P4S - perforated on all four sides
perf 12:00x12 - horiz rows of perfs are perf 12, with 2 larger diameter perf holes at intervals;
usually 11 regular perf 12 holes are between pairs of larger holes.
(PH) - Photo in center section
PM - perforated margin
pm - printer's mark. Since 1936 printer's used a tiny letter on seal #56, on sheets of 100, to identify
their product.; "E" Eureka Specialty Printing Co., "S" Strobridge Litho. Co. 1930-58, Specialty
Printers of America 1975-92 "D" Edwards and Deutsch Litho. Co., "U" U.S. Printing and Litho.
Co., "F" Fleming-Potter Co., etc.
r.9, roul.9 - roulette 9
S - Spring issue
SE - straight edge
SE4S - straight edge on all 4 sides of a sheet
Sg - smooth gum
SqBg - square broken gum - a square pattern impressed in the gum to prevent curling.
T - test seal, usually a design experiment
TB - tuberculosis
UK - unknown printer
UL - Union Label, like printer's marks, these can be used to identify sheets.
VBg - vertical broken gum, a vertical diamond pattern impressed in the gum to prevent curling.
VM - varying margin; a margin made when a cut separates a perforated press sheet into smaller
sheets or panes. Depending on where the knife cut chances to fall, such a margin will be a narrow PM, SE, or perforated edge. From 1932-62 Eureka sheets have a VM on two sides of the sheet.
x - sheet