It's important for an artist to include name, title, and contact info (phone number, email, website URL, etc.) on the back of works of art they sell. I'm in the process of cataloging the works in our art collection, and I've run into a few pieces with no indication as to how to get in touch with the artist. I think this is very important, especially when the artist signs their work using initials instead of their full names, thereby making a search on the Internet difficult if not impossible. The experience of cataloging our collection has made me more vigilant about adding contact info to my own works.—Burnell Yow!
Good point, Burnell. You know, when you look at the backs of works in a museum collection, they often have this information on a piece of paper attached by the gallery.
To your list in the first sentence above, I would add that date, medium (be very specific), and support also be included. The date helps curators place it within the artist's oeuvre and the medium and support would help a conservator fix it if anything goes wrong.