Yeah a lot of people have looked including me but most of us have not found it.
The only place I have not looked is the control module inside the door. Supposedly Ford puts a sticker on it. The manual claims it is on the main computer under the dash board, but I have not found it there nor on the struts supporting the trunk lid. Someone claimed Ford started to remove the stickers during assembly to prevent future theft.
I had the dealer read it. It costs about $100 to read and make a couple keys. Since it is just a simple computer hookup, I would think if you were in good with the dealer, you might be able to talk them in to doing it free while you have other work done.
By the way, ALWAYS have at least 3 sets of keys(so you can lose 1 and still not pay out the nose). You need 2 to have a spare made most places. If you have only 1 key, only the Ford dealer and a few key shops can do it. If you loose all your keys you have to be towed in. You also ALWAYS need at least 1 Key fob for similar reasons. I believe this is true for most LS, but know for sure it is on my 2004.
Good Luck,
Jim Henderson