As you may already have heard, Games Workshop is claiming to own the rights to the words "space marine" as a trademark, despite the fact that it has been in common parlance in the science fiction community since at least 1936, including usage by E. E. "Doc" Smith, Robert A. Heinlein, Poul Anderson and David F. Weber in some of the classics of our genre. They are despicably trying to bully M. C. A. Hogarth into changing the title of a work she wrote because it contains the allegedly-forbidden words.
I can think of several responses.
First of all, everyone who is aware of this should boycott Games Workshop's products. Their entire "40K" line is essentially based on the very same military science fiction genre which they are trying to hobble by attempting this tactic: one which unless their lawyers are uneducated imbeciles, they must know is illegal. They are hoping that we will back down, because we're a lot of silly geeks, in their arrogant minds.
Secondly, I hope that not only does M. C. A. Hogarth countersue, but that the Smith, Heinlein, Anderson and other estates, and all living science fiction military science fiction writers who have used the term sue Games Workshop for infringing their rights. Let Games Workshop spend all their money fighting this.
Thirdly, I urge everyone to use the terms "Space Marines" in every conceivably appropriate circumstance in written and video science fiction. Let them try to enforce their trademark against the universal scorn and defiance of the science fiction community.
They'll still be doing this when they go bankrupt owing to the first and second responses. And when they do, we can dance on the grave of their enterprise.