Double X Sharpie
Item Number: TA6649
The magician displays a regular Sharpie marker, stating that it is an "electronic rating pen" with a computer chip inside which rates people on a scale from one to ten. He then places a penny on the back of a spectator's hand, stating that "this is a one...the lowest you can possibly be."
With just a tap of the pen, the penny then visually changes into a dime..the spectator must be a perfect ten!