Pre-1978 no mark. There are no copyright marks. At bottom right is a printers' mark indicating the poster was printed by a union print shop and Country of origin USA.
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=Window poster for the 1937 film ''Beg, Borrow or Steal''. |Source=[https://movieposters.ha.com/itm/comedy/beg-borrow-or-steal-mgm-1937-midget-window-card-8-x-14-comedy/a/161210-52028.s?ic4=GalleryView-Thumbnail-071515# source...