It's not a swastika, it is a hammer and sickle. I agree that is a bit inflammatory. However, again, it is not completely untrue. Keller does admit to having some Marxist leanings. I am not saying he is a full blown communist though, that is a misrepresentation.
Here is a short biography of Keller's Marxist origins
The whole discussion is pretty good, but the biography starts at about the 37 minute mark.
www.worldviewconversation.com
Here is the print version, with all of the sources of the information listed.