If you need to sign a book for which you don't know the author, you can simply sign your own name and add a short, generic message such as "Enjoy this book!" or "Happy reading!" Alternatively, you could write a more personalized message about why you are giving the book as a gift or how it has impacted you, without specifically referencing the author. Ultimately, the important thing is to write something that shows your thoughtfulness and appreciation for the recipient.
