1. It's a secret message written in invisible ink.

2. "Invisible ink" effect obscures the message until the recipient swipes across it.

3. Now if this thing's in invisible ink, how do we look at it?

4. Vietcong couriers slipped into Saigon to pick up his reports, which he wrote in invisible ink made from starch.

5. I wrote ordinary letters, putting these messages between the lines in invisible ink and then sent them, via a cover address, to the Netherlands Bethel.