This is probably a bit late for anyone to utilize, but there's an interesting variation of bookmarks from the medieval period that had a rotating element and were the body of the bookmark was mounted in a sliding way on a string or ribbon. That would add a selector / exclusive text and another variable for ribbon positioning, if'n anyone feels like they're not seeing enough ways to use a bookmark for tracking variables or introducing randomness.
https://en.wikipedia.org/wiki/Rotating_bookmark