It's a MO policy: http://mathoverflow.net/faq http://mathoverflow.net/faq "We also encourage you to use your real name as your username. In your own enlightene

It's a MO policy: http://mathoverflow.net/faq http://mathoverflow.net/faq "We also encourage you to use your real name as your username. In your own enlightened self-interest, realise that participating in blogs, Math Overflow, the arXiv, and mathematical publishing are all forms of advertising for your "brand", even if that’s not your principal purpose (and hopefully it’s not). Since job applications require you to write your real name, you might as well use it everywhere else, too." The bright side is that if a Fields medalist answers your question, you know it ;-)