I've been travelling from the EU to both the US and Canada wearing a rep on my wrist without any hassle - in fact I even got compliments from the customs for my IWC 3717 v1!
However, within EU to a recent RWG GTG with a full watch box I actualy did have a small incident.. Me and my travel companion (Bionic Tim) had to somewhat butter up the airport security gal (who was a bit suspicious) @ Copenhagen Airport on the way out, but apart from that it was all gooooood! We even had 3 more pieces on our way home!
To sum it all up: I wouldn't worry too much about what's on your wrist while travelling..