This vintage license plate topper is fairly common, but so is confusion over its backstory. It was part of a program to eliminate unsafe and discourteous driving, and it was in the shape of a shell because it was sponsored by Shell Oil Company.
The program originated in the 1930s and was called the Share-the-Road Club. Its aim was to get rid of “Screwdrivers,” people whose bad driving habits and lack of courtesy caused traffic delays and stop-and-go driving. When drivers joined the club, they were presented with one of these license plate toppers. The shell was painted gold, but most of the gold has worn off the one in the photo. The three flags draped over the shell are nautical flags that, in maritime code, mean, “I am giving way.”
You can see the topper in this photo published in a 1939 newspaper. The man standing is a Shell Oil representative, and he is explaining the program to Lou Boedecker of the Montana State Highway Patrol.
It was free to join the club, and five million drivers had signed up by the first quarter of 1940. That explains why there are still so many of these shell-shaped toppers around!