The 1928 W502 issue is an enigma.  Similar in size and appearance to the ice cream cards of 1928, the W502 cards contain no information on the card which would identify the issuer.  Instead, printed on the backs of many of the cards would be plays in what would appear to be a baseball-related game, with individual play results printed on each card.  1928 W502 cards are also available with blank backs.  According to hobby researcher Al Crisafulli (wow, that's me) who conducted some research into this set some years ago, blank backs account for approximately half the population of W502s, with "One Bagger" backs such as this one accounting for approximately a quarter.  It is likely that the cards were made available by a retail store, or packaged inside some type of candy.  This Gehrig card has been graded EX/NM 6 by SGC, with sharp corners and a clean surface, slightly off-center left-to-right.  An exceptional card.