Illusory Script

You write on a scroll, paper, or some material suitable for writing, and imbue it with a potent illusion for the duration of the spell.

For you and any creatures you designate when the spell is cast, the writing appears in your normal handwriting and conveys whatever meaning you intended when the text was written. For everyone else, the words appear as if written in an unknown or magical alphabet, making them unintelligible. Alternatively, you can make the writing appear as an entirely different text, or in another handwriting and language, though the language must be one you know. If the spell is dispelled, both the original and the illusory text disappear.

A creature with true sight can read the hidden message.