It's generally forbidden for a man to wear a woman's garment, or vice versa. (Source.)
One type of wristwatch is the "men's watch". Some are blue or black. They're often bigger than women's watches.
Another type of wristwatch is the "women's watch". Some are red or pink. They're often smaller than men's watches.
So:
- Is a man allowed to wear a women's watch?
- Is a woman allowed to wear a men's watch?
If you cite sources, please preferably cite Modern Orthodox ones. Thanks!
Possibly related: "What are the opinions on men wearing a wrist watch? Is it considered beged isha?"