Jackson Pollock hid his signature inside one of his most important and valuable paintings, claims an art historian.

The American abstract impressionist is believed to have camouflaged the letters of his name within the vibrant lines and colours of his 1943 work 'Mural'.

The 20ft by 8ft canvas was key in cementing the young artist's reputation as a painter of international importance.

But its "hidden message", in a capital writing style, had never before been noticed.

Henry Adams is an art historian who has written a book on Pollock's life.

He didn't spot the signature - but his wife did while glancing at his print of Mural over breakfast.

"She suddenly said she could make out the letters S-O-N in blackish paint in the upper right area of the mural. Then she realised JACKSON ran across the entire top.

"And finally she saw POLLOCK below that," he wrote in the Smithsonian magazine.

"The characters are unorthodox, even ambiguous, and largely hidden. But, she pointed out, it could hardly be random coincidence to find just those letters in that sequence.

"I was flabbergasted. It's not every day that you see something new in one of the 20th century's most important artworks."

Mr Adams' theory has been met with a mixed response from other Pollock experts - and will be difficult to prove or disprove without submitting the painting to X-ray scans.

Pollock is known for his chaotic "splashed paint" style, but often based his work around a single figure or shape, which lends credibility to the historian's hunch.

Mural was commissioned by the art collector Peggy Guggenheim.

It is now owned by the University of Iowa, and valued at $140m.