If you're planning on hopping on a plane then you'll need a boarding pass, and that's a document with all sorts of information.
You probably won't pay attention to most of it as long as it's for the right flight, but there's a code that could appear on there which you definitely won't want to see.
The code is 'SSSS' and it's the kind of thing you'd see if you were flying to the US as it means 'Secondary Security Screening Selection' and it was brought in by the US Transportation Security Administration (TSA).
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It was introduced in the aftermath of 9/11 to flag up people that security personnel at the airport would want to take a closer look at, and it could mean you're subjected to carry-on luggage inspection, personal questioning, enhanced pat-downs and electronic device screening.
One frequent flyer who got an 'SSSS' code on their boarding pass said it was a 'real shock' to be flagged up in such a way, and she explained to CN Traveler that she'd been returning from a month away from the US in Turkey and the Republic of Georgia.
Their journey has significantly delated after a TSA agent scanned her pass and declared 'we got a quad', which is apparently the term for one of these warnings.
Ashlea Halpern explained that she and her husband were 'separated from our shoes, coats, and electronics', put through a metal detector and body scanner then given a full body pat down.
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Their hands and feet were 'scrubbed' for traces of explosives and all of their luggage was searched.
So, what are the reasons someone might get this 'kiss of death' code on their boarding pass?
Frank Harrison, Regional Security Director, Americas, explained that there isn't an official list of flight behaviours the TSA deems suspicious, but there are some actions which could end up looking suspicious.
"Many travellers unknowingly flag themselves due to inconsistent but innocuous travel behaviours such as booking a last-minute ticket or paying in cash,” he said.
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"If you exhibit behaviour that is inconsistent with your profile - say, for example, suddenly adopting a jet-setting pattern - this is a red flag and a potential alert for drug or human trafficking. Consistency is king."
Booking last minute tickets, buying tickets with cash and taking trips to places the US deems 'high risk', which is quite a lot more than it used to, are all behaviours which could end up with your boarding pass being marked and you being put through all sorts of security checks.
While passengers on watchlists should also probably anticipate this treatment, it has happened enough times to frequent fliers to become an unpleasant surprise.
Joe Harker