"Unregistered"? Blender is a registered trademark in both the US and the EU. Their brand guideline page explicitly calls out that you are not allowed to use their name in your own product: https://www.blender.org/about/logo/#trademark
Oh, huh. I assumed it was not registered since Blender uses "™" instead of "®" at the top of its homepage. I guess that's just for the logo then, not the wordmark.
Amusingly, you don't have to use either for it to be a registered trademark, it just makes it "more obvious". It also makes word marks look like corporate capitalist nonsense, so leaving it off does all of us a service =D