The ornamental design for a scarf, as shown and described.
FIG. 1 is a back perspective view of the scarf of the present invention;
FIG. 2 is a back view of the invention of FIG. 1;
FIG. 3 is a top view of the invention of FIG. 1;
FIG. 4 is a front view of the invention of FIG. 1;
FIG. 5 is a rear view of the invention of FIG. 1;
FIG. 6 is a side view of the invention of FIG. 1, as seen from the left side of FIG. 4; and,
FIG. 7 is a side view of the invention of FIG. 1, as seen from the right side of FIG. 4.
The broken lines represent stitching while the stippled circular portions represent loop and hook mechanical fasteners, each part of the claimed design.