Ok, it is that circle (filled or not) with 8 arrows coming out of it, usually stylized. It was designed by Michael Moorcock, but other people appear to be using it everywhere. In particular, I've seen it in Hexen video game. Can we use it in our games or it will get us in trouble, just like using the Beholder monster? Or maybe it is a basic geometric figure, that can not be copyrighted or trademarked?

" In order for a work to have copyright protection, it must reach a requisite level of creativity. Many logos, however, do not. Since copyright can’t protect a name, colors or the design of the logo, most simple logos simply do not have the required level of creativity to be considered copyrightable. However, many ornate or artistic ones do. "

From: https://www.plagiarismtoday.com/2010/08/12/trademark-copyright-and-logos/

The Chaos Symbol borrowed heavily from the Compass Rose design,so I doubt it is copyrightable.

You might also consider Trademark. According to some guy from the internet Moorcock said this...

" It never occured to me to trademark the Chaos sign any more than Tolkien trademarked Orcs.

I could have trademarked it at some point, I suppose, but I wouldn't want to. Games Workshop's lifting from me and Tolkien might have introduced new readers, but it's still irritating! However, there's a certain satisfaction of having added a few bits and pieces to the common culture to the extent that people actually don't know the origins of stuff and ideas they now use casually. None of that bothers me.

To me it was simply a logical sign to represent Chaos, just as the single arrow represented Law. I was looking for a way of dstinguishing the two sides. As I say, the version I prefer (which best represents Chaos) is the asymmetric version drawn by Walter Simonson for MM's Multiverse. I would never have considered trademarking something like that, anyway, since it's such an obvious and simple design. "

From: https://www.heresy-online.net/forums/wargaming-news-40k-rumors/125254-games-workshop-vs-chapterhouse-trial-underway-8.html