Guess you can't say you didn't notice your bill.
And the reason they do this is it allows the guest(s) to write something down in the notebook. I don't think anyone told us or suggested what we write in the notebook, but it was pretty clear after flipping through the first one (at the bar), that you could write whatever you wanted. A number of folks seemed to write about the food, restaurant, experience, etc., while others wrote whatever came into their heads, like this...
And we didn't know the ultimate purpose of these "love notes" until we went to the restrooms. They pull out approved notes and use them as wallpaper for the wall in the restroom hallway. So, while you're waiting for so-and-so to vacate the loo, you can read all about other people's experiences.
It gave the wall a very unique and, surprisingly, not a cluttered look.