invisible ink makes an appearance in the complaint as does Morse Code, which, of course, is pretty uncrackable.
Last two words are written in invisible ink but can be easily discerned if Australian law books are held over scented candles.
It was a time of invisible ink, and Franklin instructed this committee how to use it.
Then she happened to remember that there was such a thing as invisible ink.
He was, however, given a short, unsigned note in invisible ink for Count Nesselrode.
You might have it treated with invisible ink, or write something else in, up above.
Therefore you make those alterations with the invisible ink, and let it remain so.
"There may be writing on it with invisible ink," said one of his comrades.
We always write our most secret doings in invisible ink, made of lemon juice, so that nobody can read about them.
Lafayette took the hint, and discovered the message written with this invisible ink on the bit of paper.