At some point I though Plaid Hatter was a clever name for a game company. As it turns out, I was right. Somebody else has had a company called Plaid Hat Games for decades.
I did a little sniffing around at the Patent and Trademark Office, and term Sublight isn't being for much. And the few things it is being used for aren't game or book related. So it's safe to use for a project.
I have started a project to start mapping all references to plaidhatter to start pointing to sublight. And at some point in the near future, I'll reserve the sublight trademark.