Ehhhh. Everything can have its excess. I believe artists should always mark ownership of their own works. They've put time and effort into those pieces, no matter what medium it may be (though if we're talking watermarks then it's likely the digital drawings). I think you mark your work appropriately. Do whatever makes you feel comfortable to post your pieces online? We all know you've dealt with theft before. It's a major hassle so why not take the steps you can to discourage it? Besides, if someone wants a piece from you that's watermark free the can commission you.