I love this story from last week in The Argus, which mentions a British artist finding a slice of bacon left as a bookmark in a returned library book.
I've used all manner of items as impromptu bookmarks over the years (yarn, movie tickets, bus passes, a dollar bill), but I don't think I've ever used a food item.
And the disappointing thing is that, if this is the actual book-and-bacon combo, it's not even in a cookbook. (Then again, the way some of my most-used cookbooks look, I may have well used a slice of bacon to mark a favorite recipe.)
The funny thing is that people do seem to use food as bookmarks. The article mentions the site BiblioBuffet, which lists instances of food used as page holder. Have you ever done such a thing?