This spell enables the wizard to write instructions or other information on parchment, paper, etc. The illusionary script appears to be some form of foreign or magical writing. Only the person (or people) who the wizard desires to read the writing can do so. An illusionist recognizes it for illusionary script.
Unauthorized creatures glancing at the script must roll saving throws vs. spell. A successful save means the creature can look away with only a mild sense of disorientation. Failure means the creature is subject to a suggestion implanted in the script by the caster at the time the illusionary script spell was cast. The suggestion cannot require more than three turns to carry out. The suggestion could be to close the book and leave, or to forget the existence of the book, for example. A successful dispel magic spell will remove the illusionary script, but an unsuccessful attempt erases all of the writing. The hidden writings can be read by a combination of the true seeing spell and either the read magic or comprehend languages spell, as applicable.
The material component is a lead-based ink that requires special manufacture by an alchemist, at a cost of not less than 300 gp per usage.