The ornamental design for an armband, as shown and described.
FIG. 1 is a front perspective view of a first embodiment of an arm band showing our new design in an in-use configuration;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is a front perspective view of a second embodiment of arm band showing our new design in an in-use configuration;
FIG. 9 is a front view thereof;
FIG. 10 is a rear view thereof;
FIG. 11 is a left side view thereof;
FIG. 12 is a right side view thereof;
FIG. 13 is a top view thereof; and,
FIG. 14 is a bottom view thereof.
The broken lines immediately adjacent to the shaded area represent the bounds of the claimed design while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.