Release not dated. Seller says 1948 and given the age of Hampton in the photo, the yellowing of the release and style of it, this seems correct. It's before the mid 1960s because zone numbers are used in the addresses and no Zip Codes.
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.