Christmas is coming up. My bfs mom is a huge reader and has a big collection of books.
She let me borrow one of her personal books and I noticed she sharpied her name into it.
I saw on Etsy they make some cute ink or embossed stamps that say “x’s library” or something. They’re not super expensive and there are so many designs.
Another option are bookplates that can have more elaborate designs or even customised as they’re just stickers so might be more bang for the buck though not as reusable as a physical inked stamp.