The ornamental design for a scarf, substantially as shown and described.
FIG. 1 is a perspective view of a scarf in a configuration illustrating the design as it appears worn on the body;
FIG. 2 is a perspective view of the scarf in another configuration as worn on the body;
FIG. 3 is a front elevation view of the scarf in a flat configuration;
FIG. 4 is a rear elevation view of the scarf in a flat configuration;
FIG. 5 is a left side elevation view of the scarf in a flat configuration, with the right side elevation view being a mirror image of the left side elevation view;
FIG. 6 is a top plan view of the scarf in a flat configuration; and,
FIG. 7 is a bottom plan view of the scarf in a flat configuration.
The broken lines shown in the drawings represent environmental structure and form no part of the claimed design.