A small number (cards 1-115) of 1939 Gum, Inc. Playball cards were overprinted on the reverse and given away to generate interest in the set. But PSA didn’t designate “sample” on the card flip in its early days, like with this DiMaggio that remains in an old flip today.
To date, PSA has slabbed 30 1939 Playball #36 Joe DiMaggio Sample cards, but the one above (from a November 2001 auction catalog) isn’t included in that thirty unless it was cracked and re-submitted.
The highest-graded DiMaggio samples are a pair of Nm-Mt 8s. REA sold this one in the fall of 2019 for $3600.
More about these free sample cards and their red advertising message in the future, so don’t forget to subscribe to blog posts so you don’t miss it.