What do the proof mark EKG in a circle mean on an old percussion cap pistol?

The proof mark "EKG" in a circle on an old percussion cap pistol indicates that the firearm has undergone proof testing to ensure its safety and reliability. The letters typically represent the proof house or the specific inspector responsible for the testing. Such marks confirm that the pistol has been tested with overpressure rounds to verify its structural integrity. This mark is an important indicator of the gun's quality and compliance with safety standards during its production period.