The ornamental design for a motorcycle handle bar, as shown and described.
FIG. 1 is a front elevational view of a motorcycle handle bar showing my new design;
FIG. 2 is a side view from one side thereof;
FIG. 3 is a side view from the opposite side thereof; and,
FIG. 4 is a perspective view thereof.
The broken line showings of the handle grips, brake levers, and the mounting hardware are for illustrative purposes only and form no part of the claimed invention.