LEFT INSIDE: Celmer's Books Envelope

Another odd item I've found inside a book is this business reply envelope for a defunct used bookstore in Chicago. Celmer's was run out of a private home in the Buena Park neighborhood throughout the 60s and 70s.  When the store folded John Chandler, owner of the spectacularly messy and utterly awesome Bookman's Corner bought most of Celmer's stock. I own many vintage books from Celmer's (all purchased in John's store) and periodically I'd find one of these envelopes tucked in the back of the book.

I have no idea the purpose of the envelopes. I guess you could use them to request books from Celmer. I never asked about the use of the envelopes though John Chandler did tell me numerous stories about the woman who owned Celmer's. I've since forgotten her first name. 

The biggest mystery, however, is the Astro-Slide trademark on the envelope.

A search of the US trademark registry database reveals that Astro-Slide is a typeset trademark (basically a registered logo design) for a brand of electronically operated door mechanism. It was created and registered in 1971 and owned by a local company called Dor-o-Matic based in Harwood Heights, Illinois.  The trademark has since expired and all Dor-o-Matic products are now distributed under the brand name Falcon, a subsidiary of Allegion which is one of the largest companies involved in safety and security products (door hardware, locks of all types, burglar alarms, security systems, etc.) in the world.

But why is a used book store advertising a door mechanism on their business envelopes?

The illustration by the way is a direct copy of this famous Albrecht Dürer etching. It wasn't part of the trademark, only the font and wording was.

I don't understand the link between electronic doors and a medieval astronomer either.  Maybe I need to take more lecithin in my diet.  My brain just can't perform the kind of overtime work needed to figure out these riddles.