As a current official symbol, any national flag primarily "means" the nation it represents, with or without warts. (The warts are mainly visible beyond the nation's boundaries.) As a mute symbol, one can invest a flag with whatever deeper meaning history and society will support.

The Confederate States flag represents no current nation. As a result, it "means" on the one hand whatever those who fly it want it to mean. On the other hand it's going to mean something quite different - perhaps vastly different - to other people with different experiences.

The sign linked by McG of H is a great example of what I mean. In the American South the "rebel flag" is often taken as merely a regional symbol. Of course the "takers" are almost entirely white people who, at best, have a limited imagination and like the idea of being "rebels" of one sort or another. They like to think the War Between the States was fought not so much over slavery as it was to keep the Yankees out of their hair. During the War, most citizens of the white North were as racist as those of the white South. They just drew the line at owning slaves, partly because the North didn't have big plantations growing cotton, indigo, and tobacco, the crops that made slavery the most profitable.

I never assume that a Confederate flag must be a racist statement. Of course I never dismiss the possibility either.

For the sake of contrast, when I see the Union Jack flying in the U.S., I *never* assume it's a statement that the Queen wants the Colonies back. It could be - but that would be extremely weird. I think.