1936 publication, publishers and artists anonymous and long dead. Widely reproduced in many sources (e.g, Simon & Schuster's TIJUANA BIBLES) without claim of copyright. It was legally impossible to file for copyright for these at the time they were issued due to obscenity and other problems of legal liability (trademark infringement, slander, etc.).
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.