Christine Feehan is the author of several bestselling series, including one simply called "Dark" -- in her trademark application with the USPTO, she has applied for the exclusive right to use the word "Dark" (in "standard characters without claim to any particular font style, size, or color") in "Series of fiction works, namely, novels and books."
Literally thousands of books have the word "dark" in their titles, including several series such as Phillip Pullman's His Dark Materials and Stephen King's Dark Tower books.
In 2018, the independent author Faleena Hopkins created a stir when she trademarked the term "cocky" in connection with book titles, and then used the trademark to attack fellow authors who, it turned out, were part of a group of Amazon Kindle Unlimited writers who had colluded to boost sales by gaming the keyword system (Hopkins later lost her trademark).
Hopkins isn't alone: the Austin-based erotic fantasy author Michael-Scott Earle sought a trademark on "Dragon Slayer" in book titles, and then a trademark on any book cover featuring a person holding a weapon. (In both cases he was denied his mark).
Feehan's application has not yet been assigned to an examiner. It was filed on her behalf by Greg Mavronicolas, a New York based attorney from the Mavronicolas Law Group PLLC.
This person is trying to trademark the word "dark" so only they can use it in titles.https://t.co/FWtf5e8aze— Cat Rambo (@Catrambo) November 28, 2019
Meanwhile, on Amazon: 1-16 of over 40,000 results for Books : "dark"