Discarded delights: The joy of ex-library books (2021)

My late mother was an avid reader of library books. She used to mark the books she had read by filling in the loops of the letters on the copyright page. Apparently she noticed the hidden codes that other readers used to similarly mark books they had read: a circle around page 10, a line on page 20, &c.

I wonder if the author has come across such marks?

My late father would put a little star on the last page of the book. He eventually discovered another patron was marking books in a similar fashion and that they had the same taste in books. Whenever he found the other mark he would check out that book.

Your post has omitted the punchline.