I claim the ornamental design for a safety cover for trailer ball hitch, as shown and described.
FIG. 1 is a perspective view of a safety cover for trailer ball hitch showing my new design; the broken lines showing environmental structure being for illustrative purposes only and form no part of the claimed design
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a right side elevational view thereof, the left side elevational view being a mirror image thereof; and,