The ornamental design for the smock, as shown and described.
FIG. 1 is a front perspective view of the smock, illustrating a child wearing it.
FIG. 2 is a front perspective view of the smock.
FIG. 3 is a back perspective view of the smock.
FIG. 4 is a left side view of the smock.
FIG. 5 is a front elevational view of the smock.
FIG. 6 is a right side view of the smock.
FIG. 7 is a back elevational view of the smock.
FIG. 8 is a top plan view of the smock; and,
FIG. 9 is a bottom plan view of the smock.
The dot-dashed broken lines showing portions of the human figure illustrate the design as worn and form no part of the claim. The evenly spaced broken lines illustrate the portions of the smock, which form no part of the claimed design.