Several years ago, a professional organization of colonoscopy professionals began holding what they called a "world conference," although so far they have all been in India. They have been registering and using worldcon####.com as their web site. People contact me or the MPC asking what can be done about this. The answer is, "Not a lot, really." You see, their conferences have so far always been in India, and show no sign of being in other countries. Worldcon has never been held in India, and I'll be really surprised if it ever happens. While Worldcon is a registered service mark in the USA and EU, and is asserted as one in Canada and Australia, as long as they stay in India and we never go there, it's likely that neither of us has a valid case against the other. There's no world-wide protection for trade and service marks, and WSFS doesn't do enough business in India to justify registering there anyway. So we ignore them, and they ignore us — at least they've ignored every attempt we've made from WSFS to contact them, and they've never contacted WSFS of which I'm aware. I suggest everyone else ignore them, too.
Also, suggestions that we go out and try to buy up every plausible domain name in the form worldconYYYY.com|org|net|world|etc are not only expensive, but IMO relatively useless, given how easy it would be to evade the registration with something similar, e.g. worldcon-YYYY.com, etc.
I don't think we have a reasonable case to try to convince ICANN to prohibit any address that starts with "worldcon" anywhere in the world.