The ornamental design for a watch, as shown and described.
FIG. 1 is a front elevational view of a watch showing my new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a right front perspective view thereof.
The strap elements depicted by broken lines have been shown for the purpose of illustrating portions of the watch that form no part of the claimed design.