I am not a fan of intellectual property, either as a concept or an instance thereof.
I do recognize the need to protect yourself when you provide a service or product and someone else tries to use your good name to sell a poor imitation of the same.
That does not extend to titles of books. The existence of that kind of intellectual property would have the effect of forcing authors in our day to use nonsense words as short titles, because all the meaningful short titles would be used up -- and many reasonable longer ones would be used up, as well.
Just think. If I had an author ancestor who wrote a novel called Wind a hundred years ago and trademarked the name, and I inherited the trademark, I could keep you from writing a modern novel called Wind, and my ancestor might well have been able to prevent a certain well-known novel from being named Gone with the Wind.
Series of novels are a somewhat different matter, but I'm not sure they should be. At any rate, the courts currently accept that titling a series is more of a business practice with need for protection. Fortunately, the preexistence of the use of a word or phrase limits the reach of a trademark here, as well.
Now if I wrote a series of books about a family of inventors named "Sparky", perhaps I'd want to prevent other authors from pretending to write books in my series by trademarking the name for use with a series of books.
I would almost call that reasonable.
But here's the question:
Trademark "Spark", "Sparky", or "Sparky Clan"?
"Spark" and "Sparky" have prior use, and will have a lot of reasonable exceptions (prior use, literary, etc.) to my control. It will also tempt me to waste money and time in trying to enforce the trademark on things that I should leave alone.
"Sparky Clan", trademarked for use with a series of science fiction novels, would be pretty strong -- specifically because it is narrow. Judges and juries are much less likely to doubt my intent, in no small part because I'm going to be much less tempted to bring claims in bad faith.
Advice, if you're going to trademark the name of a series of novels or such:
Keep your trademark claims reasonably narrow.