An exlibris for my books in a digital age?

smalgin writes: While I cannot boast by an extensive library, it keeps growing every week. I share the books I like the most with my friends and acquaintances. Unfortunately, some of them are sloppy and forget to return my books, so to speak. I would like to put some mark, sticker or a stamp (Ex Libris) on my books to make them recognizable later. However, living in a digital age (blah blah yada yada) I cannot help but wonder how could I improve the ex libris beyond an ink stamp on a title page or a glued-on postcard-sized monstrosity some libraries use?

Did anyone try using RFIDs to identify his books? Please share your experience.