It's also easy to hide a watch under a sleeve or jacket if Walt was concerned about it being to "showy". I think Heisenberg has it out flaunting it on purpose. Much like when he was drunk and telling Hank that Gale is not the Heisenberg he was looking for. Dropping little hints to either taunt Hank or deep down he wants to get caught to end the insanity. eta: or a third option -- to drop so many hints and *still* outsmart Hank. Hiding in plain sight.