The proper sign for this word depends on your meaning or intent.
WRISTWATCH:
If you want to talk about a wristwatch, you can use an "F" handshape on the back
of your wrist.
The sign BRACELET could also mean "watch"
WATCH (be looking at/more detached/spectator)
LOOK-AT: (to look at something)
If you want to talk about "watch" as in "look at" you should check out the "SEE"
page for a more complete discussion of this topic. But I'll include the
main "watch/look" variations here:
"Look at that."
WATCH: (regional variation)
"Looking at." (This version is not recommended.)