What exactly is a Rack Postcard?

Answer 1

A rack card is a document used for commercial advertising, frequently in convenience stores, hotels, landmarks, restaurants, rest areas and other locations that enjoy significant foot traffic.[1] Rack cards are typically 4 by 9 inches in size and sport high-impact graphic design.
Some people collect them. For more information check out http://members.aol.com/RackCardKing/index.htm