I claim the ornamental design for a belt guard, as shown and described.
FIG. 1 is an exploded perspective view of a belt guard showing my new design;
FIG. 2 is a perspective view of FIG. 1;
FIG. 3 is a front elevational view of FIG. 1;
FIG. 4 is a rear elevational view of FIG. 1;
FIG. 5 is a bottom plan view of FIG. 1;
FIG. 6 is a top plan view of FIG. 1;
FIG. 7 is a right-side elevational view of FIG. 1; and,
FIG. 8 is a left-side elevational view of FIG. 1.
The broken lines showing an engine, a belt, and gears in FIG. 1 and text and a logo in FIGS. 1-3 depict environmental matter and form no part of the claimed design. The broken lines in FIG. 4 depict portions of the rear side of the belt guard that form no part of the claimed design.