From http://olympus-entertainment.com/forum/index.php?/topic/1518-11-2-2014-updates/
Specifically:
Real World Extremist or Terrorist names are not allowed
I can't believe I'm defending the name ISIS but I think this is a very slippery slope. How do you define Extremist? We have guilds named BlackWater, and after seeing the real life version of them I would quite willingly call them Terrorists. I'm not trying to be a angst ridden liberal here. The idea of Terrorist is being slung around all over. If a guild is named IRA, is that a terrorist group? All depends on who you ask.
I'm a former Marine and hate, HATE the real organization ISIS for what they represent and their actions. However, I think that we're really screwing with free speech here if we pass arbitrary rules like this. It specifically targets one group of people while leaving plenty of room for free and easy interpretations in the future. It's really risky and I think someone should pause and think about the future potential for abuse.