SEC. 18. Every gun, rifle, or weapon of any kind, or ammunition, found in the possession or custody of any free negro or mulatto, not having a license as required by the preceding section, may be seized by any person, and upon due proof thereof made before some justice of the peace of the county in which such seizure was made, shall by order of such justice be forfeited to the use of the person making the seizure, and such justice shall also impose a fine on such negro or mulatto, for the use of the county, not exceeding twenty dollars.