During an exhibition game against the Chicago White Sox on September 9, 1931, Hartnett was photographed while signing an autograph for gangster Al Capone. After the photograph was published in newspapers across the United States, Hartnett received a telegram from Baseball Commissioner Kenesaw Mountain Landis instructing him not to have his photograph taken with Capone in the future. Hartnett replied with a telegram to the Commissioner whimsically stating, "OK, but if you don't want me to have my picture taken with Al Capone, you tell him."