A book with highlights, margin notes, and sticky notes is a completely different object from a pristine copy of the same title. The marks tell you how someone reads — and why.
What annotations signal
People who mark their books are active readers. They're engaging with the text, not just consuming it. This is almost always a signal of serious study or intellectual habit.
- Heavy annotation → student, researcher, academic, serious learner
- Sticky notes on non-fiction → professional development, active application of ideas
- Highlights in fiction → literary reader, writer, or writing student
The volume of marks matters
One or two underlines per chapter is light engagement. Margin notes on every page, cross-references between books, colour-coded systems — that's a researcher or an obsessive. The density of marks is its own signal.
Dog-eared pages
Dog-ears without other marks usually mean a casual reader who didn't want to lose their place. It's a weaker signal than annotations but still indicates the book was actually read.