The ornamental design for a label, as shown and described.
FIG. 1 is a perspective view of the label;
FIG. 2 is a front plan view of the label;
FIG. 3 is a rear plan view of the label;
FIG. 4 is a side view of the label;
FIG. 5 is a top view of the label; and,
FIG. 6 is a bottom view of the label.