A113 is a recurring media easter egg created by alumni of the California Institute of the Arts. The number refers to the classroom used by the graphic design and character animation students.
This easter egg appears multiple times throughout the movie.
In the scene when Lightening McQueen is racing after “Mack”, but is about to be cut off by a quickly approaching train, the camera cuts to the trains face revealing the trains number as A113.
In the scene right after Lightening McQueen paves the road correctly and the townspeople(cars) are expressing their amazement at how smooth it is, Tater the tow truck can be seen driving in-front of Luigi’s tire shop where he briefly shows his rusted license plate. If you pause and look hard enough Taters license plate actually says, “A113”.