Challenge: Best Bookmark Ever! Answered

 Bookworms often have a lot of use for this nifty device, now lets take it to it's the next evolution! 
Ladies and Gentlemen, this is a new era we are about to unfold...
I challenge someone to come up with the best possible bookmark that is:

A. Possible

B. Useful

C. Won't ruin book/ Still is a bookmark

No need for an instructable (although would be epic), I just challenge you to come up with a design and explain your design thoroughly and how normal everyday bookworms might make this device.

Ideas:
Highlighter Pen
Pencil
Paragraph indicator (where you are on page)
Non-tearable
Not heavy
A way to make it STAY on page
...