The following information on police badges and protective coats comes from Section 59 of Shooting by J. Henry FitzGerald. Shooting is also available to purchase in print.
The standard police badge of today has two distinct uses: one to denote the rank of a police officer and the other to point out the exact location of the officer’s heart to the law-breaker. A badge or cap ornament may be readily seen at night in a dim light when otherwise the officer would, as far as shooting at any particular spot to shoot at, be invisible. I hope that in the near future an oxidized or dark colored badge will be adopted.
Many police departments have adopted a Sam Brown belt and holster worn on the outside, and I believe this is the proper place to wear a revolver for police use. If, however, the arm is worn on the inside, at least the two lower buttons on the coat should be snap buttons that coat may be quickly opened in case of need. If a small revolver is worn in the overcoat pocket said pocket should be lined with heavy canvas or leather and pocket so built that hammer spur will not catch as arm is drawn. The test as to whether arm is carried in a correct position for quick work or not is this: Can you stand, hands at side, revolver in holster or pocket, and get into action, firing the first shot in less than two seconds and hit what you aim at? If this can be done then the position of revolver is nearly correct. Besides position of revolver, practice enters into this demonstration, but an officer’s life is not safe in case of trouble unless he can do this.