Of course, now that you have posted the block for the entire world to see, your odds of success in defending a copyright for the block itself are somewhere between slim and none. If you write a pattern, don't publicize it before you register the copyright. Here's an overview of how to do that.
http://www.copyright.gov/help/faq/faq-register.html
It's $35 to file online, $65 to file paper forms. Current e-filing processing time is roughly 2.7 months (paper filing is 6.1 months).
http://www.copyright.gov/eco/