Reddit reviews House of Marbles : Invisible Ink UV Light Pen – Spy Pen
We found 1 Reddit comments about House of Marbles : Invisible Ink UV Light Pen – Spy Pen. Here are the top ones, ranked by their Reddit score.
House of MarblesInvisible Ink UV Light Pen – Spy PenOne Spy Pen per package
You might try using a UV pen to put a few dots on the back of a card, on the border? You’d have to see how the “invisible” ink interacts with the coating on the card, but that might be the least obtrusive way to do it.
https://www.amazon.com/dp/B0160CVWEE/