The ornamental design for a scarf, as shown and described.
FIG. 1 is a perspective view showing a scarf of this design when in use being worn by a person;
FIG. 2 is a front view of the scarf of this design;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side elevational view thereof; the right side is a minor image of the left side;
FIG. 5 is a bottom elevational view thereof; and,
FIG. 6 is a top elevational view thereof.
The dotted lines showing a person's arms, torso, neck and head in FIG. 1 are for illustrative purposes only and relate to elements which do not form part of the claimed invention. They illustrate the claimed design in use. The broken lines shown in FIGS. 1-3 illustrate stitching and are part of the claimed invention.