Though originally hand painted, one by one; the art, and posters created by the WPA were eventually designed to be massed produced by way of silkscreen printing. This created a unique graphic style which became associated with American design and art of the late 1930's/ early 1940's. I have always envisioned certain portions of "Topaz" to make use of this style.
The images shown on this post are from the Library of Congress collection By the People, For the People: Posters from the WPA, 1936-1943. The collection consists of 908 boldly colored and graphically diverse original posters produced from 1936 to 1943 as part of Franklin Delano Roosevelt's New Deal. Of the 2,000 WPA posters known to exist, the Library of Congress's collection of more than 900 is the largest. These striking silkscreen, lithograph, and woodcut posters were designed to publicize health and safety programs; cultural programs including art exhibitions, theatrical, and musical performances; travel and tourism; educational programs; and community activities in seventeen states and the District of Columbia. The posters were made possible by one of the first U.S. Government programs to support the arts and were added to the Library's holdings in the 1940s.
Here are some highlights from the library of Congress collection: http://memory.loc.gov/ammem/wpaposters/highlights.html