The ornamental design for a headband, as shown and described.
FIG. 1 is a perspective view of the headband.
FIG. 2 is a front view of the headband as shown FIG. 1.
FIG. 3 is a back view of FIG. 1.
FIG. 4 is a left side view of FIG. 1.
FIG. 5 is a right side view of FIG. 1.
FIG. 6 is a top view of FIG. 1.
FIG. 7 is a bottom view of FIG. 1.
FIG. 8 is a perspective view of first alternate position of the headband as shown in FIG. 1.
FIG. 9 is a perspective view of a second alternate position of the headband as shown in FIG. 1; and,
FIG. 10 is a perspective view of a third alternate position of the headband as shown in FIG. 1.
The dashed lines in the drawings depict portions of the headband that form no part of the claimed design. The dotted lines in the drawings depict stitching and are included in the claimed design. The long dash lines in the drawings followed by the short dash lines depict the boundary line of the claimed design.