I claim the ornamental design for a massage pin, as shown and described.
FIG. 1 is a perspective view of a massage pin with environmental structure shown in broken lines;
FIGS. 2 and 3 are further perspective views of the massage pin;
FIG. 4 is a side view of the massage pin;
FIG. 5 is a front end view of the massage pin;
FIG. 6 is a rear end view of the massage pin;
FIG. 7 is a perspective view of the massage pin according to another embodiment of the present design, and showing a connecting end of the massage pin and environmental structure in broken lines;
FIGS. 8 and 9 are further perspective views of the massage pin;
FIG. 10 is a side view of the massage pin;
FIG. 11 is a front end view of the massage pin; and,
FIG. 12 is a rear end view of the massage pin.
The broken lines portions shown in the drawings are for illustrative purposes only and form no part of the claimed design.