Here Are the Four Most Dreaded Letters on Your Boarding Pass

The code "ssss" for Secondary Security Screening Selection on a boarding pass. "Close up on the SSSS" by Jason Eppink/Flickr ll CC BY 2.0 ( ept.ms/2haHp2Y

If you see “SSSS” written on your boarding pass, you may be in for some trouble at the airport.

Boarding passes labeled with this code subject their carriers to extra scrutiny, costing them time and possibly their flight, if they don’t arrive at the airport early enough.