What do you use for a bookmark?

My niece who reads more than I do, opened a book I gave her from my Newbery stash last November or so...and found the giftcard I'd given her for Christmas 2006--thankfully it still worked & she got a nice blouse. I sent her a $20 for her birthday with a post-it on it saying "This is NOT a bookmark."

What do you use? As a library worker, I have found some odd things...Airline tickets (always, unfortunately, used), receipts (never for anything I could return myself for profit), those fake credit cards you get in the mail attached to solicitations for new accounts (never the real thing, sigh), bills (hopefully paid already), bandages (uh, gross!) and then today...I find in one book: a list of bank transactions, medical records (carotid ultrasound), and a bus schedule. I kind of thought I could chart the guy's day...I feel like I've violated HIPPA by just opening a book!

Oh, and the librarian in me feels beholden to say "If you dogear the pages, remember we know where you live."