Turns out you can call a TSA agent an idiot and nothing happens.
Added to clarify:
I have Pre and it is printed on my boarding pass, otherwise I could not enter the Pre line. They check for the "Pre" stamp both when I enter the line, and when they scan the pass at the end of the line. After that point, I put away my ID and boarding pass and enter a "reduced screening" line (the point where they check your baggage and send you through the metal detector).
What I'm saying is that at my airport, they sometimes also direct non-Pre passengers (who've had their boarding pass checked via a separate line) into the same "reduced screening" line. At that point, both Pre and non-Pre passengers are receiving the same "reduced screening".
It is at this point where I've had the metal detector randomly flag me for going through the image scanner. When I protested that I had Pre, their response was "we don't have any way to know that at this point").
Pre almost always saves me time, so it's not a racket in that sense. But it is a racket in the sense that it's no guarantee you won't end up with a pat-down. It's theater in the sense that: either the government trusts me, or they don't. If they don't trust me, they shouldn't have issued me Pre. If they do trust me, then I shouldn't need to be patted down.
BTW: the security at SFO is not TSA. It's a TSA approved contractor (Covenant Aviation Security). I think Tampa is also that way.
It does. Three beeps from the little scanner thingy at the ID check means you have Pre. One beep means you don't.