These are super hero leveled library signs that I use in my classroom. Each level stands for a guided reading letter (pink-F, orange-G, yellow-H, green-I, white-J... etc.) I then use yard sale dots to label my books. Students are then able to pick books at their own level, and are responsible for returning them to the book bin with the corresponding sign.
Let me know if you have any questions, or email me if you want me to make you one that is slightly different for your own leveled library!
Note: This would also work for a DRA leveled library.