I have no idea how or when my fetish came to life. In fact, as a child I hated wearing watches myself! I was well in my teens before I got my first watch, a Swatch, but even at that time I didn't feel any reaction to women wearing Swatch or other watches. Even to this day Swatch does nothing for me. I remember going through christmas catalogues and home-shopping/coupon catalogues noticing the watches, but when it actually became a fetish, I simply don't remember.
I do however clearly remember the first time a girl was involved. Through a friend of a friend I met this cute girl, who was wearing a Casio rubber strap diver, kinda like this one:

At that time (1990) it was an unusual watch for a girl to wear (later they became a short-lived hype, tho). Not only was she an extremely cute girl, the sporty but not boyish type, but this huge watch on her wrist made her even more interesting. I asked her why she wore a watch like that, and all she said was something like "because I like it."
We went out a couple of times (even went to see "Pretty Woman"... in the theatre! LOL!) but we never got really involved. She was definitely my kinda girl, but I guess I wasn't her type, and eventually we lost touch. She was one of the biggest crushes of my life, and I still think of her sometimes.
I guess from that experience I realized there was a connection between the girl and the watch she wore. It began to matter. Someone wrote earlier "I am on the constant lookout for woman wearing large steel watches when in public rather than looking at a girls face. First right wrist, left wrist then face." I can relate; the first thing that attract me may not always be her watch, but I definitely check. If she's wearing a watch I don't like she's not interesting to me at all!
Because of that, I have been open about my fetish with all my girlfriends, without exception. I don't necessarilly tell them it's a fetish in sexual terms, more like an "interest". For instance, I've never asked any of them to wear a watch in bed, because I don't need them to. But it matters to me what they wear, and I have succesfully turned them into wearing watches even though none of my girlfriends were really "watch persons" when I met them. They've all been great with my "interest" and loved when I gave them a new watch.
All I can say is, if you have a fetish, almost any kind except for the really creepy ones maybe, be open about it. It's worth it. Nothing worse than having a fetish you feel you can't share with your soulmate. You don't need to sit her down and come clean all at once. Comment on something you see in public or in TV; if you see a girl wearing a nice watch, say something like: "hey, that looks kinda cool, don't you think?" and see what she says. From there, it becomes easier. And hey, you're not asking them to wear latex and beat you with a rotten fish. It's just a watch.