Actually a name would be a trademark. This you could do, very easy really. I mean it, my brother is starting up a custom guitar buisness and so I know about that stuff. I think he told me it was $300 to register a name as a trademark. It would be the same as the name Burger King, or Paramount. If its the username you want ot lock,so no one else can use it legally on some site and then make others think its your work,then thats the way. Just be warned its tough to stop everyone,but registering it as a trademark can be done. http://www.uspto.gov/