It's called the SOPA bill:
http://en.wikipedia.org/wiki/Stop_Online_Piracy_ActIt's a law to stop online piracy, but it has many flaws that could cause the law to be abused and lead to sites like Omnimaga, Facebook or Youtube to be blocked in United States and possibly other countries.
Some sites on Jan 18th are perfoming a blackout to protest against that bill, so those sites will be temporarily closed between 8 AM and 8 PM that day. I don't think Omni is doing that, so this most likely explains why there's only a small banner.