Dateline: Boston -- Impersonating an Author?

Stopped in at a Borders in Cambridge, on the way to the Apple Store, and asked one of the managers if she'd like me to sign copies of KILLER INSTINCT. She gave me a dead stare and said, "If you can show me a picture ID."

I said, "You're kidding, right?"

She said, "No, I'm not. New store policy. Some people sign other people's books."
So what I'm now wondering is -- just who the hell goes into bookstores and signs books they didn't write?