PE = Pioneer Era [1893-1898]

Government postcards with no pictures. Any pictures were hand illustrated, not commercially printed.

PM = Private Mailing card [1898-1901]

Government gave permission to private printers to print and sell postcards with the inscription “private mailing card”.

UB = Undivided back [1901-1907]

All correspondence had to be written on the front of the card, not being allowed to have a divided back.

DB = Divided back [1907-1914]

Left side was for messages, the right side for addresses.

WB = White Border [1915-1930s]

Usually printed in tinted half-tones partially for style, partially due to ink shortages at the end of WWI. The white border gave more leeway when cutting down the postcard sheet.

LE = Linen Era [1930-1944]

Printed on a linen texture paper, using brightly colored inks.

CE = Chrome Era [1945 – current]

They are known for high photo quality and true living color. They generally have a glossy coating.