Roger Ebert has a tongue-in-cheek Movie Glossary with entries for various movie tropes and clichés. I didn’t know this bit of trivia though:
All movies set before 1955 should have yellow and black stop signs.
From the Wikipedia:
Stop signs originated in Detroit, Michigan in 1915. The first had black letters on a white background and were somewhat smaller than the modern one. As they became more widespread, a committee supported by AASHO met in 1922 to standardize them, and it selected the octagonal shape that has been used in the US ever since.The unique eight-sided shape of the sign allows drivers facing the back of the sign to identify that oncoming drivers have a stop sign and prevent confusion with other traffic signs.
In 1924, the sign changed to black on yellow, the predominant color until 1954. Another competing group, the NCSHS, simultaneously advocated an even smaller, red-on-yellow stop sign. All of these signs were typically mounted only two or three feet above the ground.
These two organizations conflicted but eventually combined into the Joint Committee on Uniform Traffic Control Devices, which in 1935 published the famous Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD) detailing the stop sign’s appearance. The MUTCD stop sign was altered eight times between 1935 and 1971, mostly dealing with its reflectorization and its mounting height; the most drastic change came in 1954, when the sign gained its white-on-red color. Red is also the color for stop on traffic signals, unifying red as stop signal for drivers worldwide.
The mounting height reached its current level of seven feet in 1971.