The ornamental design for a pocket for attachment under the arm of a sleevelessundershirt, as shown and described.
FIG. 1 is a front elevational view of a pocket for attachment under the arm
of a sleeveless undershirt showing my new design, the broken lines showing
the undershirt throughout the views are to illustrate the placement of the
claimed pocket only and forms no part of the claimed design; and the
broken lines shown on the claimed article itself is understood to
represent stitching;