This is a reputation-building magic and a very good publicity stunt. You show an opaque black bag and put it over somebody’s head. He cannot see anything through it, not even a single ray of light. You wear it and the strings are tied around your neck. Blind folded in this way, you can drive a car, a bike or a cycle through the busiest street of the town. You don’t make any accident and stop in front of a red traffic light. Of course you need to know how to drive them unless you already know it.
A black bag is handed to a spectator who is asked to place it over their head.
They attest they can see nothing but black- no light at all.
The magician then takes the bag and places it over his/her head and asks the spectator to write anything (perhaps on a large dry-erase board). The magician is able to write the exact same thing- he must have X-Ray vision!