The item has no copyright marks as can be seen in the links. At bottom left is "C"-for poster version "C", (Version D is in the Congo Maisie article.) Litho in USA and (looks like) #9375. At lower 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.