Your gait as your signature!

What about this? Interesting article on how 'gait recognition' could be used by spy satelite.

"Spy satellites could soon be able to identify someone from space by looking at their shadow.
They would use a computer program that searches for the movement of shadows on the ground, and then identifies their owners from the way they walk. The technique - called gait analysis - relies on the fact that someone's walking style is very difficult to disguise."