I am reading “Chavs: The Demonization of the Working Class” by Owen Jones. Borrowed from my local library, a previous borrower has made their own addendum.
It reads “keep them out of mischief“.
There are lots of these. Some reinforce points (or disagree). Some are checking the author’s arithmetic. Why make notes in a borrowed book? There’s not enough time to read it twice and it is unlikely you would borrow the same copy (there’s a waiting list).
My favourite – “Hazel Blears” always annotated “Chunky Kit-Kat“.