There are no copyright marks on the poster. This is seen at the links above and on the upload which is not cropped. At bottom left is Country of Origin USA; at bottom right is Morgan Litho Corp., Cleveland, O. 14383. The number appears to refer to the print job of 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 1938 film ''Heroes of the Hills''. |Source=[http://www.ebay.com/itm/Heroes-of-the-Hills-One-Sheet-Movie-Poster-The-Three-Mesquiteers-Western-1938-/201233888857?pt=LH_DefaultDomain_0&hash=item2eda797659&nma=true...