The ornamental design for a sock, as shown and described.
FIG. 1 is a left side view of a sock showing my new design; and
FIG. 2 is a right side view thereof; and
FIG. 3 is a front view thereof; and
FIG. 4 is a rear view thereof; and
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof;
FIG. 7 is a left side perspective view thereof; and,
FIG. 8 is a left side perspective view thereof in a position of use.
The evenly dashed lines in FIGS. 1, 4, 6, 7 on the left side of the sock depict claimed portions of the design. The broken lines in FIG. 8 are illustrative of environmental structure forming no part of the claimed design.