Sooner or later, as an article author… you must make your way to: http://copyright.gov/ to investigate and/or register how to copyright your articles or your compilation of articles.
Most legal counsel would advise you to not even think about throwing stones at those who would rip you off until you had a registered copyright on your works. (of course, I’m not a lawyer, so consult yours first before taking my advice.)
Almost everyone I know who has ever produced a book registers their copyright — but it’s not all that common for article authors to register their copyright.
Basic copyright registrations are $30 USD.
Have you ever registered a copyright for any of your articles?