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.

Attractive, blank-backed card of Hall of Famer Frankie Frisch.  Light surface abrasions are visible on the card front which, along with writing on both the front and the reverse, reduces the numerical grade. Despite the wear and writing, a visually pleasing example.