The 1926-29 Exhibits "Postcard Back" issue is speculated to have been issued in the Philadelphia area.  Though the cards typically feature postcard backs, they are occasionally found blank, and some with the notice "Not for use in Exhibit Machines."  Further, some contain a country of origin (USA) added to the backs.  The cards can be found printed in a variety of color tints as well.  The result is a wide variety of possible variations with differing degrees of scarcity, very appealing to advanced hobbyists.

Midgrade example exhibits some light corner rounding with a faint area of staining along the top edge.  Reverse shows some mild toning.  Small white dot on Traynor's show that appears in the scan is on the scanner glass and not on the card.