Disappearing-ink pen

The disappearing-ink pen is an ordinary-writing pen featuring a special ink which will disappear after a given amount of time. 

This pen is a perfect personal protection device to safeguard you against bad people who might threaten you and try to force you sign documents against your will.

A three-stage picture is provided to show pen effectiveness, as follows:

1. the disappearing ink pen has just written "CIAO HELLO!" on a paper;
2. shows the writing 30 minutes later;
3. shows the writing 60 minutes later.