Spotting the letters “SSSS” printed on a boarding pass can be unsettling, especially if you’ve never seen them before. Many travelers immediately worry that they’ve been placed on a watchlist, done something wrong, or could even be prevented from boarding their flight. The unfamiliar code has led to countless rumors online, leaving many passengers anxious before they even reach airport security.

In reality, the meaning behind those four letters is much less alarming. SSSS stands for Secondary Security Screening Selection, a designation used as part of aviation security procedures. While it does mean you’ll receive additional screening before boarding, it is not a sign of guilt or suspicion. The reason you received it may surprise you.