I claim the ornamental design for a safety guard, as shown and described.
FIG. 1 is a perspective environmental view showing a safety guard according to the design mounted to a ladder, the ladder being shown in phantom and forming no part of the design;
FIG. 2 is a top view of the design;
FIG. 3 is a view of one end of the design;
FIG. 4 is a rear view of the design;
FIG. 5 is a side view of the design, the opposite side being a mirror image thereof; and,
FIG. 6 is a view of the opposite end of the design.