To be valid, a hanging permit must be clearly visible and hanging from the rearview mirror post of a vehicle. The permit number must face the windshield. A permit must not be defaced or altered in any way.  If you purchase an adhesive permit, it must be clearly visible on the driver's side rear bumper or on the back of the rearview mirror. On a motorcycle, the adhesive permit must be affixed to the rear fender of the motorcycle.