Here is a 'busy' cover which I find interesting, a Special Delivery airmail to Canada, 26 cent franking, and a nice Rockefeller Center Cinderella on the back. I also find the 'If not delivered Sep 29, please return' instruction unusual. I am wondering if this type instruction was allowable by US/Canadian postal regulations? I also wonder if the sender meant to it only to be delivered on Sep 29 or if they actually meant 'if not delivered by Sept 29?
See this thread for another Rockefeller Center Cinderella http://goscf.com/t/50242
I see both examples appear to be booklet stamps. This basic stamp design was also used for the 1934 New York Stamp Exhibition as shown here.