The ornamental design for a side sill for a vehicle, as shown and described.
FIG. 1 is a front right elevated perspective view of a side sill for a vehicle according to the present invention.
FIG. 2 is a front right perspective view of the side sill shown in FIG. 1.
FIG. 3 is a rear left elevated perspective view thereof.
FIG. 4 is a rear left perspective view thereof.
FIG. 5 is a front view thereof.
FIG. 6 is a rear view thereof.
FIG. 7 is a left side view thereof.
FIG. 8 is a right side view thereof.
FIG. 9 is a top view thereof.
FIG. 10 is a bottom view thereof; and,
FIG. 11 is a front view of the side sill for a vehicle shown in FIGS. 1-10, but with the side sill mounted on a vehicle shown in broken lines. More specifically, the broken lines form no part of the claimed design, but are instead included to show environmental aspects thereof.