Even without paying cash, anytime I've purchased a ticket at the airport the day of flight my boarding pass has been marked for additional TSA security. Although, it has been a couple years since I've purchased at the airport, so maybe things have changed. (Once walked into CVG as my phone rang, asking if I could get to DFW instead of going home. Another time this happened at MDW. I've switched airlines, and purchased tickets, at LAX, LAS and MCO and also been subject to the "SSSS" on my BP. Come to think of it, I haven't had "SSSS" on my BP, or seen anyone with it on a BP, in a couple years.)