Publishers Little, Brown have released a cover shot ahead of the publication of The Casual Vacancy on September 27, showing what looks like an X on a ballot paper with a red background.
The 512-page novel, the writer’s first for adults, is about an idyllic town ripped apart by a parish council election.
A spokesman for booksellers Waterstones said: “While it is great to see such a bold cover image, it’ll cause frustration among those desperate to find out more about the plot. There are no clues here. As ever, the JK Rowling guessing game continues.”
The book is set to be a bestseller with shops already reporting high pre-order demand.
It begins with the unexpected death of Barry Fairbrother, whose demise in his early 40s leaves a space on the parish council.
Little, Brown said it would be a “blackly comic, thought-provoking and constantly surprising” novel.
Rowling has amassed a fortune estimated to be in excess of £620 million from her seven Harry Potter books for children and teenagers, plus all the spin-off rights.
This will be her first novel since the final chapter of the Potter franchise was published in 2007.
The books have sold more than 450 million copies and have been translated into 74 languages.