Not sure how many people have heard of the book series / television series by this name, but can somebody explain the grammar behind the name "The Vampire Diaries"? Does it mean "the diaries of the vampire"? If this is the case, shouldn't it be "The Vampire's Diaries?
"Vampire" is acting as an attributive noun. These are diaries that are related in some way to vampires, or a vampire. They could be diaries written by vampires, or describing events concerning a vampire. They could even be diaries that will suck your blood.
Attributive nouns can sometimes be replaced by a prepostional phrase. But you can't tell which preposition would be used without more context.
So "the vampire diaries" could mean "the diaries for a vampire" or "the diaries about a vampire" or "the diaries of a vampire" or "the diaries with a vampire" etc. etc.As with other forms of ambiguity in English, this rarely causes any problems, but can be used for jokes.
Would you like some girl-scout cookies?
Are they made from real girl scouts?