I walked into the TSA screening area on a Delta return flight this week, not even having glanced at my boarding pass, walked up to the podium, and the guy said, "Sir you have precheck. Take this card, and you don't have to take off your shoes".

I thought he was confused, but you don't question those kinds of things. Precheck was nice by the way. I was flying with others, and they didn't have it, but it did in fact say on my boarding card "Precheck". Aren't I supposed to apply? Aren't they supposed to charge me a fee, and search my background (clean - but don't they check). I was left confused. Can somebody explain what happened?

When I fly other airlines, will it still say precheck on my boarding card, or will I actually have to apply?