The SSSS (Secondary Security Screening Selection) code is assigned by the U.S. Transportation Security Administration (TSA) through its "Secure Flight" passenger pre-screening system. While the airline prints the code on your boarding pass, the decision is made by the federal government's automated risk-based algorithms. You may be selected for several reasons: booking a one-way international ticket, paying for a flight in cash at the last minute, traveling from a high-risk country, or simply being chosen via random selection. The system matches your name, date of birth, and gender against various government watchlists, including the FBI’s "Selectee List." If you have SSSS on your pass, you cannot check in online or at a kiosk; you must see an agent to verify your documents. At the security checkpoint, you will undergo an enhanced screening process that typically includes a full-body pat-down, a thorough manual search of all carry-on luggage, and swabs of your hands and electronics for explosives residue.