The ornamental design for a taillight for a vehicle, as shown and described.
FIG. 1 is a front right perspective view of a tail light for a vehicle, showing my new design;
FIG. 2 is a front left perspective view thereof;
FIG. 3 is a rear right perspective view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a front right perspective view of the tail light for a vehicle shown in FIGS. 1-6, with the tail light mounted on a vehicle shown in de-emphasized and half-tone portions so as to illustrate environmental structure. These portions form no part of the claimed design. More particularly, in FIG. 7, the tail light is shown within the broken line, and the elements shown outside of the broken line form no part of the claimed design, but are instead included to show environmental aspects thereof.