When a trademark is owned, you have a legal obligation to chase behind the use of it. In this case the name is not trademarked, and as @ew-and-patterns states you cannot trademark too common words. They state that we profit of their good name, which is also something we could argue against because it's provably the own community that immediately switched and there is no profit to speak of to any specific or non-specific owner of the name.

I was thinking of the iOS situation that Apple sublicenses of Cisco as an example on how to deal with this peacefully, but when they don't have any trademark to begin with, I think the best way to go is call their bluff as any of us personally and maybe make a clear disclaimer instead, possibly working together to make each other stronger.

Even more, the company structure is an Ltd, which is a company structure in the USA that cannot use their name without mentioning the Ltd. We legally don't use the same name in any way, they are HIVE Blockchain Technologies Ltd., this blockchain operates under the concept of Hive that had prior art on Steem itself to indicate the community.

That said, I am not a lawyer and I can imagine that this won't be the end of it. But I am really interested if they want to go forwards with this whom they will appoint as representing the blockchain.