We claim the ornamental design for a shackle, as shown and described.
FIG. 1 is a perspective view of a shackle made in accordance with an embodiment of the new design;
FIG. 2 is a side view of the shackle of FIG. 1, the opposite side being a mirror image of FIG. 2;
FIG. 3 is a front view of the shackle of FIG. 1;
FIG. 4 is a rear view of the shackle of FIG. 1;
FIG. 5 is a top view of the shackle of FIG. 1;
FIG. 6 is a bottom view of the shackle of FIG. 1;
FIG. 7 is a perspective view of a shackle made in accordance with another embodiment of the new design;
FIG. 8 is a side view of the shackle of FIG. 7, the opposite side being a mirror image of FIG. 8;
FIG. 9 is a front view of the shackle of FIG. 7;
FIG. 10 is a rear view of the shackle of FIG. 7;
FIG. 11 is a top view of the shackle of FIG. 7; and,
FIG. 12 is a bottom view of the shackle of FIG. 7.
The portions of the Figures shown in phantom lines are not part of the claimed design but are for either illustration only, or to define the boundaries of the claimed design.