In January of this year, my wallet was stolen (or maybe I lost it...) in Philadelphia, so I didn't have any ID and had to go through security. I did have a photocopy of my passport, but they didn't really count that as a legit ID.

At security, they asked me to sign my name and just kind of compared it to the signature on my photocopy. Then I had to go through the normal secondary screening/pat down.