FIG. 1 is a perspective view of the motorcycle taillight. FIG. 2 is a front elevational view of the motorcycle taillight. FIG. 3 is a top plan view of the motorcycle taillight; and, FIG. 4 is a side elevational view of the motorcycle taillight with the opposite side being a mirror image of the same. The back forms no part of the claimed design. The broken lines form no part of the claimed design.