When I was in college getting my teaching degree in English, one of my favorite professors said a true reader can't read without a pen. I love books, and for a while I thought writing in them was somehow taking away from their value. I was wrong. Writing in books and flagging pages isn't being disrespectful. It's the complete opposite. You're showing your love for the story.
Getting permission to write in the margins of the books I read was like heaven to me. I started underlining, dog-earing, and even writing comments in the margins. Even when I read on my Kindle, I use the notes and highlights features while I read. It lets me find favorite passages and record my thoughts.
Now to be completely honest, for my favorite books, I have more than one copy. One to write in and mark up and the other to display on my shelf. In fact, sometimes I've been known to buy three copies so I have the book in every format.
How do you show your love of books? Do you write in them, make notes on Kindle, buy more than one copy, etc?