Paperbacks of Dashiell Hammett began in the late 1930s according to my research. Albatross edition of Maltese Falcon looks to have been published in the mid-1930s. Of course, Dell and Pocket Books started publishing Hammett in the late 1930s and early 1940s. Of course, after the famous John Houston adaptation of The Maltese Falcon appeared in 1941, paperback editions of Hammett took off. A full list can be found in Warren's Official Paperback Price Guide.
I like the later 1960's versions of Hammett covers because they are designed so well. The UK editions are interesting, too. The Penguin paperback with the bulldog on the cover is pretty neat. More recent versions of Hammett (mostly in trade paperback form) either use crime photos or graphic design on the covers. I think I prefer the graphic design covers.
Ian Ballantine was a young graduate student in 1939. He wrote a thesis on the economics of the paperback industry in the late 1930s that brought him to the attention of several paperback publishers. He opened the American branch of Penguin Books (a UK company) in 1939. Ian was primarily responsible for re-selling Penguins in the United States. However, World War 2 cut off his shipments from the UK, so he began to publish paperbacks himself. One change he made was to add illustrated covers to his paperbacks which were primarily sold through magazine distributors and needed an eye-catching cover to compete. But when Penguin founder Anthony Lane visited the U.S. Penguin offices after the war, he was appalled at these new illustrated covers. He demanded that the paperbacks be simply text and be color-coded like the British Penguins. Ian Ballantine refused and left the company. Ian started his own company with his wife Betty Ballantine and secured funding from a major hardback publi...