The ornamental design for an armband, as shown and described.
FIG. 1 is a top perspective view of an arm band showing our new design in a flat configuration;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a side view thereof;
FIG. 5 is an opposite side view thereof;
FIG. 6 is a right side view thereof; and,
FIG. 7 is a left side view thereof.
The broken lines immediately adjacent to the shaded areas represent the bounds of the claimed design while all other broken lines arc directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.