I can't vouch for the authenticity of the picture, signature or mild act of vandalism it represents. A reader sent it in to NBCDFW.com, alongside other claims that the Giants had treated the shiny new locker room with disrespect. I will admit, though, that if Eli had left his signature on the new building, I'd find it pretty damn amusing, as well as an indication of an ornery side of Eli that I didn't know existed.
The signature does look like Eli's, though that doesn't rule out some Photoshop magic. Eric Kreindler at the Blue Star wasn't able to get anyone in the Cowboys organization to respond to questions about it.
I'm going to choose to believe it's real, just because life is more fun that way. It's amusing, too, to picture Jerry Jones being alerted to the signature, turning red, and then wondering if there's any way he could get away with having Eli killed.
Gracias, Blue Star.