The ornamental design for watch dial, as shown and described.
1. Watch dial
1.1 : Front
1.2 : Back
1.3 : Perspective
1.4 : Right
1.5 : Left
1.6 : Bottom
1.7 : Top
Reproduction 1.1 is a front view of the watch dial; reproduction 1.2 is a back view of the watch dial; reproduction 1.3 is a perspective view of the watch dial; reproduction 1.4 is a right side view of the watch dial; reproduction 1.5 is a left side view of the watch dial; reproduction 1.6 is a bottom view of the watch dial; reproduction 1.7 is a top view of the watch dial.