I believe Linus owns the Linux trademark? In any case, there is no maintaining of the trademark, as anyone can build off of the Linux code and call it "* Linux". Because there is no enforcing of the trademark, it's doubtful whether it can still be used to do anything.
In practical terms, someone could make something called "TotallySecure Linux", but which actually contains spyware, and I'm not sure Linus (or whoever owns the Linux trademark) could do anything about that.
But this doesn't really matter, because Linux isn't a consumer brand. The people that actually use Linux - like us - know enough to not be confused by a "TotallySecure Linux". But that isn't the same for VLC and Firefox.