The ornamental design for a sock, as shown and described.
FIG. 1 is a front and top perspective view of a sock, showing my new design;
FIG. 2 is a rear and bottom perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof; and,
FIG. 9 is an enlarged view of a portion indicated in FIG. 1.
The dash dot dash broken lines shown in the figures are for the purpose of depicting the cut line of the enlarged view and form no part of the claim. The evenly dashed broken lines shown in FIG. 7 are for the purpose of depicting a portion of the sock and form no part of the claim.