The item has no copyright markings on it as can be seen in the links above. At bottom left is "C" (poster version) Litho in USA, and a number which appears to pertain to the printing of the poster. At bottom right is Tooker Litho Co. NY-they printed the poster.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (50 p.m.a.), Mainland China (50 p.m.a., not Hong Kong or Macao), Germany (70 p.m.a.), Mexico (100 p.m.a.), Switzerland (70 p.m.a.), and other countries with individual treaties.
{{Information |Description=Poster for the 1939 film ''Another Thin Man''. |Source=[http://www.thethinman1934.com/anotherthinmanposters.html site] |Date=[http://www.imdb.com/title/tt0031047/ 1939] |Author=MGM |Permission=Pre-1978 no mark |other_versions...
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