That is an aftermarket mirror that is similar in style to the original. There were two styles of outside rear view mirrors for the 1951-55 Kaisers. One is a clamp-on mirror part #100142 that mounted on the door edge ahead of the vent window and the deluxe mirror was mounted on the door below the rear of the vent window, part #100143, Illustrations are on Jim Betts site. Parts and Accessories Bulletin 4-A April 14, 1951 They are apparently the same as used on the fifties Hudson and are very difficult to locate.