It’s a good time to do a checkup on our understanding of trademark law concepts.
One is a reminder that a book or movie title alone cannot be trademarked, but a series of books with the same title component can. That component need not be at the beginning (“… for Dummies” is a legitimate wordmark). My “Do Ask Do Tell” series (three books) would probably enjoy a common law mark, but it would not be exclusive. That follows from the fact that the books have been in commerce since 1997 (with the first one). It is not necessarily clear that company or business names or Internet domain names have to match. It appears that both authors and publishers can claim such a brand concept. I don’t find anything in the literature so far that claims that the “business” has to be financially self-sustaining on its own, or that it can’t be a closely held proprietorship. However, most book and movie series trademarks are owned in part by large publishers, or movie studios or even comic book companies, with most of them publicly traded. In practice, it is usually possible for a trademark attorney to find out how effective a mark really is as a brand from financial records of publicly traded companies. But that would seem to have a political motive (how many people’s jobs are affected) than one having to do with consumer confusion over brands, which is what trademark is supposed to be about.
A good reference on trademarks and series is here.
It's also accepted trademark law that businesses in different industries or “classes” can have the same mark. However, the USPTO tends to deny duplicate marks in “other” classes if USPTO thinks consumers are likely to be misled anyway. The way media gets distributed and branded online today (as well as diverse financial models, from “it’s free” to ad-supported to subscription) complicates what used to be straightforward branding concepts, and makes consumer of public reactions much
harder to predict.
Here is a reference on Quora and on Legalzoom.