It was originally intended to be a joke; but I disagree with luchog when he implies that it was the white supremacists who were being trolled. The target of the joke was supposed to be SJWs, and the intention was to get them to freak out over a very common everyday hand-sign.
That's very likely as well. I think it will depend on the motivations of the particular individuals involved in it, though; and like most 4Chan/Something Awful/etc. hoaxes, it's a lot of people doing it for different reasons as some sort of accelerated fad. That's how most stuff works there, or at least, it did. Someone would have an idea, a bunch of others would jump on it, it would mutate and develop, and eventually escape into the real world. And by the time it achieved meme status in the wider landscape, the original crowd had already latched onto something else.
This situation serves to make a point I've tried to make in the past - which is, ultimately there's little meaningful difference between "just trolling" and genuine racism as the Venn Diagram approaches the shape of a single circle. Some users of sites like 4chan still like to (to a lesser and lesser degree these days) pretend that they're not "really" white supremacists, just faking it because they like how mad it makes people. There may have been a point when that was true, but it was long ago; the place is now filled with legions of "genuine" white supremacists, and the "jokes" and memes are no longer exaggerated racist/extremist tropes and caricatures, they're now just very plain and quite standard white-supremacist propaganda.
Yeah, pretty much. I used to be a /b/tard back in the day; and 4Chan has evolved, or devolved depending on your point of view, a lot in the last dozen years or so. It used to be just (deliberately) "humans with all the filters removed", and a lot of different ideas and memes fermented there. It was partly responsible, along with similar site Something Awful, for the explosion of the cat caption phenomenon. Content varied from light and silly, to sick and degenerate, to mind-bendingly surreal. Incidentally, that's where the Brony fan developed. It originate on 4Chan per se, but the site provided the nucleus that the fandom coalesced around and exploded outward from. A lot of good stuff came from there, and a lot of bad stuff. One of the largest anti-Scientology movements started there, for example.
Sometime around the middle of President Obama's second term, the site started to go rapidly downhill. /pol/ became the home of the soon-to-be-name-alt.right racist fringe, and they spread out and effectively took over the rest of the site. It appeared to correlate roughly to the emergence of the Gamergate controversy and subsequent explosive outpouring of misogynist ranting.
The expansion of sexism, racism, and nationalism on 4Chan, like that on Facebook and Reddit, appeared to ramp up in the run-up to the presidential election, and I strongly suspect it was part of that same Russian troll factory responsible for it getting as bad as it did. Not that it wasn't bad already, but it was certainly fed and cultivated fairly extensively.