Here is a fun post on Marty Roesch new blog - I especially like this one:
Security Sauce: Airport Security: Meatspace Intrusion Detection: "Once you extend that signature [what TSA screeners have to look for] set to, well, pretty much everything that's not paper or cloth you're going to have an analysts nightmare because you just did the equivalent of 'alert ip any any -> any any (msg: 'Something bad may have happened!!';)' in Snort. "
What is even more scary is this: the more the TSA screeners look for nail clippers and hair gel, the more likely they are to miss a gun or a stick of C4. Think about it! That is just how humans work (or, rather, fail!)