Bookplates, such as the one pictured below, were for many years a way for a book owner to mark their ownership of a book, and, according to the Virginia Historical Society, “reassure the owner that a borrowed book would be returned”. As seen in the picture, they would often contain a picture or design, the owner’s name, and the words “ex-libris”, or “from the library of” (Dictionary.com). This is part of a long tradition of finding ways to ensure a book’s return, ranging from simple messages in the medieval era to more modern methods like the one seen in the picture. Bookplates became less popular as the 20th century progressed, though some continue to collect and create them.
However, bookplates could and do have modern applications. They could be a great way to add your own personality to a book, while at the same time providing a way for a lost or borrowed book to be returned to its owner: in this respect, they could also include contact information. Creating your own design is possible by finding an example on the internet to use as inspiration, tracing one from your own book collection (this might be an excuse to visit the local rare bookstore), or by designing your own. An interesting update to the practice would be using a photo or digitally designed image to create the design for your bookplate. Print it out on high-quality paper and use some glue or other adhesive to attach it to the inside of the front cover of a book.
The alternative to this is the supralibros, mentioned here, which would also be possible to create for yourself, though more difficult. These were gold, stamped coat of arms placed on books, a practice still continued today in some cases. It would be possible to make your own with some tracing paper, a design, seal, or coat of arms in mind, and some gilding paint or gold foil.