http://edition.cnn.com/2013/05/02/tech/innovation/future-of-design/index.html

I wonder why these devices are always depicted to be placed on the hand or wrist. Wouldn't it be more practical to have these tatoos be done on the forehead, since most airports and public security systems are using face recognition to identify a person. If you have the face already in view, you could read the tatoo from the same image. And since a tatoo could be invisible to the eye, but visible to the machine it would not be a problem for esthetic reasons.

But then again, if anyone would have believed 100 years ago that this technology would exist in the near future, they would have declared that person insane.