The ornamental design for a taillight for a vehicle, as shown and described.
FIG. 1 is a left, front perspective view of a first embodiment of a taillight for a vehicle according to the design;
FIG. 2 is a front view thereof;
FIG. 3 is a left side view thereof; and
FIG. 4 is a top view thereof.
FIG. 5 is a right, front perspective view of a second embodiment of the taillight for a vehicle according to the design;
FIG. 6 is a front view thereof;
FIG. 7 is a right side view thereof; and,
FIG. 8 is a top view thereof.
The broken lines in the drawings illustrate environmental subject matter only and form no part of the claimed design. Also enclosed is a set of photographs of an embodiment of the design.