The ornamental design for a scarf, as shown and described.
The sole FIGURE shows a top plan view of a scarf.
The inner dot dash dot broken lines surrounding the scarf represent the boundaries of the claim and form no part thereof. The claim is directed to the portion within the inner broken line boundary. The dot dash dot broken lines and the lightly shaded portions outside of the inner broken line boundary represent environmental subject matter that forms no part of the claimed design. The claim within the inner broken line boundary is intended to be used as a repeating pattern. The design is flat and planar; depth forms no part of the claimed design.