I found this:

A113 (sometimes A-113, A-1-13, A1-13 or A11-3) is an inside joke and Easter egg in media developed by alumni of California Institute of the Arts, referring to the classroom used by graphic design and character animation students including John Lasseter, Tim Burton, Michael Peraza, and Brad Bird. Bird first used it for a license plate number in the "Family Dog" episode of Amazing Stories. It has appeared in most of Pixar Animation Studios films and other Walt Disney Pictures films.

Bird said, "I put it into every single one of my films, including my Simpsons episodes—it's sort of my version of caricaturist Al Hirschfeld's 'Nina'."

Classroom A113 is currently the first-year graphic design studio's door number.