The ornamental design for a lamp for a vehicle, as shown and described.
FIG. 1 is a perspective view of a lamp for a vehicle showing my new design, with the center portion of the claimed design broken away to indicate indeterminate length;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is an enlarged view of portion 8 in FIG. 1.
The broken lines in the drawings are included for illustrative purposes only and form no part of the claimed design.