These are called book belts, which are similar to book marks, but have a piece of elastic that wraps all the way through the inside of the book to hold your page. They are really cool because they're not as easy to loose as bookmarks, and you can make them as elaborate as you want since the decoration is held on the outside of the book.
I made mine out of dominos that I altered. The images are from an old Stampin' Up hostess set called Organic Grace. I used acrylic paint, gold leafing, and embossing powder to add details to the Stazon-stamped images. I also added in some gold wire as embellishment. After finishing the dominos, I attached ribbon and completed the belt with a piece of elastic that is only seen on the inside of the book and holds your page. You can see the elastic in the last picture.
I will say that next time I make these I will probably go for some chord elastic and find a nifty way to attach it to the ribbon so it looks nicer, but I'm happy with these and they will get lots of use! My two oldest daughters have already claimed their favorites.