One of the reasons I wrote the column was that I think there's a lot of misunderstanding in the writing and publishing community about what a trademark is, along with what can and can't be trademarked, and what it means to register (as opposed to own) a trademark. I've tried to explain those concepts clearly in the column.
The trademark issues in relation to book titles/series has been in the news, and the blogosphere, a lot recently because of the April 2018 trademark registration granted to romance author Faleena Hopkins over the term "Cocky" as a registered mark for her series about the "Cocker Brothers". (Bottom line - you can't own or register a TM for a book title, but you can sometimes register a mark in relation to a series where the mark is clearly operating as a source identifier for the series. The fact that something is registered does not mean that the registration is valid, and this particular registration is currently being challenged by a number of people and organizations.)
At the beginning of June, a NY court handed down a decision about the mark. There's been a LOT of misunderstanding about that decision and it has been misquoted in a number of places. It is definitely good news for people concerned about the registration of the Cocky mark, but the court did NOT say that the mark was not valid, nor did it cancel the mark's registration.
The court DID say that the mark was a "weak mark" at best and that other authors using "Cocky" in single book titles was unlikely to confuse purchasers of romance books (consumer confusion is the basis of trademark infringement law which is why that last point is important.) The Guardian has a nice summary of what the case actually held here.
The upshot is that the mark is still registered to Hopkins and that the cancellation petitions are still proceeding and will be decided in due course by the United States Patent and Trademark Office (USPTO). However, in the meantime, authors who write books with "Cocky" in their titles can take some comfort in the fact that they have a strong argument that they're not infringing Hopkins' mark, assuming the mark to be valid, which is another thing that the courts have not yet decided definitively.
I hope this helps to clarify some of the misunderstandings out there in the blogosphere. Trademark law is actually not that difficult compared with, say, copyright law. But the use of marks for book series, particularly marks that aren't all that distinctive, is one of those little corners of trademark law that can be a little confusing for folks who don't know a lot about trademark law. If you do want a basic primer on some of the key issues that arise in this space, have a look at my column and/or to the blog post I quote there written by a TM expert. Hopefully all this info is at least a little bit helpful.