PEN § 16380

As used in this part, “chamber load indicator” means a device that plainly indicates that a cartridge is in the firing chamber. A device satisfies this definition if it is readily visible, has incorporated or adjacent explanatory text or graphics, or both, and is designed and intended to indicate to a reasonably foreseeable adult user of the pistol, without requiring the user to refer to a user’s manual or any other resource other than the pistol itself, whether a cartridge is in the firing chamber.