TSA is facing criticism for secretly tracking Americans on flights.

[dixiegrrrrl]

The "Quiet Skies" programme reportedly uses an unknown algorithm to flag flyers without any criminal record for surveillance on domestic flights.

details of that are in the story, but these are the things Air Marshals are trained to notice as "signs of a terrorists":

According to TSA internal documents published by the Boston Globe, air marshals observe passengers for a number of behaviours including:

Excessive fidgeting
Excessive sweating
Cold penetrating stare
Wide open, staring eyes
Face touching
How much they sleep during a flight
Using a smartphone

https://www.bbc.com/news/world-us-canada-45011347

[Sherman A1]

1. Another reason to avoid flying

And security theater.