SEC. 119. It shall not be lawful for any person or persons to carry or have concealed about their persons any deadly or dangerous weapons, such as daggers, air-guns, pistols, bowie-knives, dirk knives, or dirks, razors, razor-blades, sword-canes, slung-shots, or brass or other metal knuckles, within the District of Columbia; and any person or persons who shall be duly convicted of so carrying or having concealed about their persons any such weapons shall forfeit and pay, upon such a conviction, not less than twenty dollars nor more than fifty dollars, which fine shall be prosecuted and recovered in the same manner as other penalties and forfeitures are sued for and recovered: Provided, That the officers, non-commissioned officers, and privates of the United States army, navy, and marine corps, police officers, and members of any regularly organized militia company or regiment, when on duty, shall be exempt from such penalties and forfeitures.