I've never seen this graffiti before. From what I can see, I see the Star of David in there, so I'm assuming that it must be related to Judaism, the pessimist inside thinks it might be anti-semitic. I also see a 4 in there, but it might be one of those fork shapes above the Star of David unfinished. I also see some sort of diamond shaped G inside of the Star of David. So my best guess is that this is some gang with a name that begins with G that is anti-semitic, and this is their symbol. But that's just the best thing I can come up with after just seeing this graffiti for the first time 5 minutes ago. Who knows.