UV Pen Marker uses Invisible Ink This Invisible Ink pen allows police to detect, identify, and return stolen property fast in the event of a burglary. You simply mark your valuables with your name and phone number. This pen will mark all surfaces including glass, paper, wood, plastic, and cloth with permanent, invisible ink. Under ultraviolet light the marks become clearly visible to police, detectives, and pawn shops owners. One pen will mark over 1,200 valuables. Can also be used to write personal messages that will only be readable under a UV light. Although invisible to the naked eye the ink becomes visible under black or ultraviolet light. 60 Day Guaranty.