At school, they use reader covers to protect their books when they bring them home. Perhaps you had them too. I had one when I went to school but it was covered with boring contact. The girls teacher told us we could decorate them anyway we wanted.
Esther and Ellamay love girly stuff like ballerina's and princesses. So we covered their reader covers accordingly. We used their favourite outfits from some paper doll books they had and stuck their photo on and then covered with clear contact.
I think they look super cool. Everyone will know who they belong to.
We used the same technique for their birthday party last year. They had a princess party (of course) and I printed out a bunch of dresses and they picked what they wanted. They made some art for their wall. Very easy and cheap and a great way to use the paper dolls clothes up when the paper doll loses her head - which ALWAYS happens.