Ruth, the artist's name is José Antonio Madrazo. The bartender at El Pegaso was ready to murder me because I made him write it down while he was in the midst of a busy Saturday lunch hour.
It so happens that the artist runs a mail order site for the sale of Mexican folk art here. Push "Click to Play" in the upper left middle of that page.
If you let this page load completely you will see a little slide show of nichos, which is what the little boxes are called.
Unfortunately, the nichos in the slide show are boring and in no way representative of the delightful pieces that I saw in the restaurant.