Everyone has their own secret, invisibility potion pen can protect your secret from finding by others, and has multiple uses.
In poker, there is a kind of cheat playing cards, processed with invisible potion ink. There are some players buying the invisibility potion pen or invisibility potion printer to make the cheating cards by themselves. Invisibility Potion pen can also be used for the following situation.
Using in the paper that you are inconvenient to writte something.
Your signature bill or marking your precious things to protect from loss.
Using in company confidential letters, protecting company trade secrets.
Using in alternative letters, the real content can not see by others.
Using in security marking, not only on paper, but also written on the body, on the wall and so on.