All of my currently published books (and future books will be) are registered with the Authors Guild Human Writer Licensing Program, and each has a unique registration number.
Books that are licensed and registered as 'Human Authored' through the Authors Guild will have the "Human Authored" trademark symbol and carry a legal license with legal repercussions for falsifying this claim.
How to know if a book is legally licensed as "Human Authored"-
This licensing program is now available to all traditional publishing houses and Indie authors who can meet the "Human Authored" requirements. Registered books will have the official Human Authored trademark on the front or back cover OR the Human Authored registration number on their copyright page as many authors can not redo covers to add it to already published work.
If there is 'human authored' language on the copyright page, there must be a registration number or the trademark symbol with it, or it is not legitimate. The cost is free for Guild members (up to 10 books) and $10.00 per book for Non-Guild members (one-time fee).
If you would like books written by authors who have made a commitment not to use AI in their writing, and are willing to legally attest as such, these are the indicators you are looking for.
The Unicorn Shore: The Secret of the Shell
Human Authored Reg #: 3065554, https://authorsguild.org/human
The Unicorn Shore: Eclipse's Secret
Human Authored Reg #: 7963989, https://authorsguild.org/human
The Unicorn Shore: The Ring of Mischief
Human Authored Reg #: 3903278, https://authorsguild.org/human
Who Are The Authors Guild?
"The Authors Guild is the nation’s oldest and largest professional organization for published writers. Since our founding in 1912, we have served as the collective voice of American authors, and have long supported the rich and diverse literary culture of our country. Our members include novelists in all genres and categories, nonfiction writers, journalists, historians, poets, and translators. The Guild welcomes traditionally-published authors as well as self-published, independent authors.
We advocate on behalf of working writers to protect free expression and ensure authors have enforceable intellectual property rights; we fight for fair contracts and compensation; and we provide a welcoming community for writers and translators of fiction, nonfiction, poetry, and journalism.
Our educational and charitable arm, the Authors Guild Foundation, helps support our advocacy, offers programming to teach working writers about the business of writing, and hosts literary events that highlight the importance of a rich, diverse American literary culture and the authors that contribute to it."
Quoted from the Authors Guild website: https://authorsguild.org/about/