The ornamental design for a headband, as shown and described.
FIG. 1 provides a front perspective view of an embodiment of a headband in place on the head of an infant.
FIG. 2 provides a side perspective view of an embodiment of a headband in place on the head of an infant.
FIG. 3 provides a right side elevational view of an embodiment of a headband.
FIG. 4 provides a left side elevational view of an embodiment of a headband.
FIG. 5 provides a top elevational view of an embodiment of a headband.
FIG. 6 provides a bottom elevational view of an embodiment of a headband.
FIG. 7 provides a front elevational view of an embodiment of a headband; and,
FIG. 8 provides a back elevational view of an embodiment of a headband.
The broken lines showing a human head on which the headband is placed and the bows on the headband are for illustrative purposes only and form no part of the invention.