Size and shape and maybe usage is what separates a bookmark from a tag. Lately I've been making my own 'base' tag or mark from manila file folders or cardstock. I've got several examples to use for shape/size patterns.
Sometimes I will round the corners or use decorative scissors around the sides or sometimes just at the bottom end. Occasionally I'll use a stencil template to give the bottom a creative touch.
Inking the edges also gives distinction and can help reinforce your selected color palette.
Here are some of my recent attempts: