WTF?
Firstly, if you don't want someone to steal it surely the sensible thing to do is make it as hard as possible for them to do that. Surely you wouldn't leave your front door unlocked with a massive TV in sight, then think that writing your name on it is going to deter someone from stealing it.
Secondly, if they remove the watermark (which I could do in about 10 minutes work) how are they going to look like an idiot? Nobody is going to know the mark was even there.
Thirdly, this isn't really the place to get into an argument over watermarking or idiotic behaviour.