I take the opposite approach: I sign my reviews and have ever since I was a grad student. It compels me to do a better job reviewing and often leads to further discussion and sometimes collaboration with the authors. Some people don't like what I have to say, but by and large, they respect it. For many topics that I review for, the authors will have a pretty good idea that I wrote the review unless I am intentionally vague. I would rather write clearly and directly and stand behind it. It is a professional risk that I don't think anyone should be compelled to take, but I think signing reviews is generally good for science.