One of my favorite movies is "Road to Perdition." In one scene you see a view of downtown Chicago looking along the Chicago River, with the bridge for the "el" crossing the river. Then you see an elevated train cross the bridge.
The problem? The elevated train has modern-day, stainless steel cars, a design that wasn't in existence in the 1930s, when the movie is supposed to be taking place. Back then the el cars were painted green.