I've been mulling over how these words are floating around on the web. It is Latin for "Thus always to tyrants" or something to that affect. Since it is most famous for having been shouted by John Wilkes Booth as he killed Abraham Lincoln, and supposed (by some) to have been said by one or more of Caesar's assassins, the implication is that tyrants always are, or should be, killed.
Why this phrase? A huge segment of the American public has convinced themselves that Obama is the worst tyrant ever to "reign" in America. Google the phrase and you will get 100s of thousands of links which at a first look seem to be to right wing blogs, etc.