I sometimes highlight, or more likely underline and annotate, but most often I mark pages with dogears or scraps of paper with the initial line of the passage I'm marking just below the edge of the scrap. Sometimes the scraps have things written on them.

Most of the time, I don't remember what my little notes were directly in relation to. Anyway, the book I pulled from my shelf was The Acid House by Irvine Welsh. The passage was marked with the following scrap of paper:

I don't know whose handwriting is, but I very vaguely remember reading The Night of the Hunter. Maybe an old roommate made the recommendation?

Anyway, the passage was the final two paragraphs of this short story:

and marked like this:

For me, this is interesting because I don't remember this story, but I do remember loving The Acid House and I know I've read through it several times. It also fits in with my fascination of human interactions and they play between the written word, perception and reality, so I wonder if this story has in fact been working on my subconscious for years and years while my consciousness has forgotten about it amid all the other stuff I chuck into my head.

Good question.