I claim the ornamental design for a set of tacks, as shown and described.
FIG. 1 is a perspective view of the first embodiment of the set of tacks showing my new design;
FIG. 2 is a side view of the first embodiment of the set of tacks showing my new design, the design being identical when viewed from any side;
FIG. 3 is a perspective view of the second embodiment of the set of tacks showing my new design;
FIG. 4 is a side view of the second embodiment of the set of tacks showing my new design, the design being a mirror image when viewed from the opposite side;
FIG. 5 is a perspective view of the third embodiment of the set of tacks showing my new design;
FIG. 6 is a side view of the third embodiment of the set of tacks showing my new design, the design being a mirror image when viewed from the opposite side;
FIG. 7 is a perspective view of the fourth embodiment of the set of tacks showing my new design; and,
FIG. 8 is a side view of the fourth embodiment of the set of tacks showing my new design, the design being identical when viewed from any side.