An infrared light that makes a stamp on a the hand visible

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An identification system uses an invisible ink or substance stamped on the hand, which becomes visible under infrared light. Infrared radiation, associated with heat, does not necessarily increase the temperature of the stamped area. There is confusion regarding whether the visibility of the stamp is due to infrared or ultraviolet light. Such technology has been in use for over 40 years, indicating its established presence in identification methods. Clarifying the type of light used is essential for understanding the mechanism behind the visibility of these stamps.
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I read about a type of identification system in which a person's hand is stamped with some sort of ink or substance that is invisible to the naked eye. This normally invisible stamp on the human hand is visible under an infrared light. I remember that an infrared camera sees things that give off heat. Apparently infrared radiation is heat radiation.

I don't think the stamp makes the hand hotter. How would the invisible stamp on the human hand be made visible by infrared light?
 
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Are you certain that is is not ultraviolet light? Such stamps/scanners have been around for at least 40 years.
 
Perhaps what I read about is ultraviolet light.
 
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