The Confidential Resource

MOSSAD PEN

This writes like a normal pen, but if you heat the paper the written words disappear. Putting the paper in the freezer makes the words reappear.

RUSSIAN KGB DISAPPEARING INK PEN

This pen features a special gel ink developed by real KGB scientists during the Cold War (and made in Russia), that disappears completely. Because it is a gel pen, you don’t need to press hard which prevents paper indenting.

UV Sensitive INK PEN

I guess every good spy needs to have his missives disappear, but I  need to secretly mark documents for later reference.

Pens like this have been  around for quite some time.  The Fisher Space Pen was at one time offered with UV Sensitive Ink refills. I occasionally use UV sensitive ink to mark important documents for security purposes.