The ornamental design for a head covering, as shown and described.
FIG. 1 is a perspective view of a head covering with the broken line showing of a head for the purpose of illustrating environmental structure and forming no part of the claimed design;
FIG. 2 is a front elevational view thereof with the broken line showing stitching;
FIG. 3 is a rear elevational view thereof with the broken line showing stitching;
FIG. 4 is a right-side elevational view thereof with the broken line showing stitching;
FIG. 5 is a left-side elevational view being thereof with the broken line showing stitching;
FIG. 6 is a top plan view thereof with the broken line showing stitching; and,
FIG. 7 is a bottom plan view thereof with the broken line showing stitching.