The ornamental design for a medical armband, as shown and described.
FIG. 1 is a perspective view of my new design for a medical arm band in a typical environment;
FIG. 2 is a front, right perspective view of my new design for a medical arm band;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a right side elevation view thereof; and,
FIG. 8 is a left side elevation view thereof.
The broken lines in FIG. 1 depict environmental subject matter, and the broken lines in FIG. 4 depict portions of the medical arm band that form no part of the claimed design; the broken lines form no part of the claimed design.