This actually happened to me at LGA this year.

I showed Brainiac my Illinois DL. Now this license is almost eight years old (sticker renewal) and is very worn. I have had absolutely no problems at any other airports using it (save a few comments on how old or worn it looks).
Brainiac uses his super-secret blue light on it and then asks me for additional ID. I refuse. He can't believe that I don't have any other ID. So he writes something on my BP and lets me go.

Now at LGA, you are required to show your boarding pass to enter the gate from hell (as has been reported here many times). No other airport requires that, but I guess to be super safe, they want to make sure that nothing fishy happend in the 50 feet from the first ID checker and the mag.

Thankfully, I prinited out another BP from the kiosk and flashed that to the gatekeeper. He let me go though.

Now the person in front of me at the initial check was also asked the same thing/ He actually showed the droid another ID. He also had something written on his boarding pass. As I was gathering up my belongings, I saw that he was pulled over and made to go through a secondary.

Glad I had the second boarding pass. And so glad that the second droid really looked carefully at the BP. Couldn't even take the time to see that it wasn't initialed bythe first one.

Damn, I feel safer just typing this out.