That doesn't make much sense either. Certainly Jews wouldn't be itching to put a metaphorical Star of David on their usernames? Historically that was not a good thing. I can see why Neo-Nazis would jump on it, but it seems strange for members of the community to voluntarily brand themselves in such a way.

I just got why it is six parenthesis though, just like the 6 pointed star.

It's a way of fucking with neo-nazis in turn. The three parentheses were originally meant as a sort of euphemism or code: rather than be publicly anti-semitic, people would put the parentheses to highlight how often Jews were being heard from, the idea being that once you notice the amount of Jewish voices around, you'll think this can't just be a coincidence (hence the name "Coincidence Detector.") It wasn't meant to be something those not in the know would get.

Jews putting three parentheses around their own names is a way of saying "I see what you're doing. I'm onto you." And non-Jews doing it is just to mess with them.