The ornamental design for a taillight for a vehicle, as shown and described.
FIG. 1 is a left perspective view of a first embodiment of a taillight for a vehicle according to my design;
FIG. 2 is a right perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a left side view thereof; and
FIG. 5 is a top view thereof.
FIG. 6 is a right perspective view of a second embodiment of the taillight for a vehicle according to my design, with the taillight for a vehicle for the opposite side of the vehicle being depicted in the first embodiment;
FIG. 7 is a left perspective view thereof;
FIG. 8 is a front view thereof;
FIG. 9 is a right side view thereof; and,
FIG. 10 is a top view thereof.
The broken lines are for illustrative purposes only and form no part of the claimed design.