Books can use the unown font if you change their NBT data. The Bookshelf mod has a command to do this automatically.
An overview of the characters in the font.
Starting with 1.19.2 you can purchase the Unown banner template from wandering traders. This will let you create banners with all letters of the unown alphabet.
The title command can be used to display text on the users screen with the unown font applied.