Have you ever...

purchased a classic book like oh what the heck let's just say Catch-22
from a used bookstore
and clearly it was used in some one's high school or middle school English class.
it has all these sentences highlighted and notes that don't quite make any sense to you. So, you spend your entire time reading the book trying to figure out what all of the highlights and notes mean an why they are so important. Is there a motif you are missing? Is there some subtle subtext that must be way over your head?
I think it would be awesome to sell a book back to a used bookstore with random highlights and notes scribbled in it. Maybe every 3rd paragraph would have two sentences or words highlighted and thinks written like
"remember page 4 quiz Tuesday!"
"recurring themes see chapter 7"
or even "so true!" on a random page.