Here is a terrific photograph from the Library of Congress, showing a traffic policeman at 14th and Pennsylvania, making use of a rearview mirror. The photo was taken some time in the 1920s.
![Policeman using mirror to direct traffic at 14th St. and Pennsylvania Avenue](https://ghostsofdc.org/wp-content/uploads/sites/7/2013/04/3b42604u.jpg)
Here is a terrific photograph from the Library of Congress, showing a traffic policeman at 14th and Pennsylvania, making use of a rearview mirror. The photo was taken some time in the 1920s.