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