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