My favorite part of the Great Movie Ride is the part in the ride where the gangster hijacks your vehicle and there's definitely a lot going on in that scene. After all, Imagineers love to put as much detail into a scene as possible. One such detail is in this scene on the car that drives up and starts shooting it out with the gangsters on the other side of the street, namely Mugsy, Squid and Beans. The license plate on the car is special because it has a special significance.
The license plate says "021-429", which is an important number in gangster lore. You see, that is the date of the infamous St. Valentine's Day Massacre (February 14, 1929) where there were two gangsters dressed as police that raided a meeting, four men in regular clothes followed and then opened fired on the group. The men in regular clothes were lead out by the "police" in what appaeared to be them arresting the men that really opened fired.
Like the other elements throughout the ride that use aspects of famous movie to build the overarching theme of the attraction, this date from history is used to add to the flavor of the Great Movie Ride.