This factory manufactured trigger guard is for the American Gun Company (New York) Knickerbocker hammerless double shotgun in 12 gauge and is in very good condition exhibiting a grayish brown patina with light wear.  This trigger guard has the notch located on the inside.  (file photo)

Note: American Gun Company Knickerbocker shotguns with the following serial numbers have been observed with this part:

12 gauge: 194426