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.

Pink-tinted, "plain background" variation of George Sisler's card, which is also found with a full photographic, uncrossed background.  The card has been graded VG/EX 4 by SGC, due to light corner rounding, most notably at the bottom right.  Some chipping is also visible in that area, though the card is quite appealing regardless.