In September 2014, an inspector with the California Bureau of Firearms made a surprise visit to Tracy Rifle and Pistol, a gun store in Northern California. He spent the next few days confirming that the business was in compliance with state regulations. After completing his audit, the inspector met with owner Michael Baryla to discuss his findings. The businessman had become accustomed to the inspections, which take place about once a year. Then came something unusual.

Mr. Baryla was directed to remove three vinyl decals on...