What's at the lower left is "made in USA". There are no other visible marks.
To be sure the poster is in the public domain, a search was done for original registrations in both motion pictures and artwork for the year 1935; nothing pertaining to Iwerks, Powers, or Celebrity Productions was discovered. There's no evidence that this material was ever under copyright.
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Public domainPublic domainfalsefalse
This work is in the public domain in the United States because it was published in the United States between 1929 and 1977, inclusive, without a copyright notice. For further explanation, see Commons:Hirtle chart as well as a detailed definition of "publication" for public art. 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.