The world's most expensive autograph is that of William Shakespeare.

There are only six known authenticated copies of his autograph, one on a conveyance for a house in London, one on a deposition in a legal case, one on his mortgage papers, and three in his will, all are held in institutions.
Should one of William Shakespeare's autographs ever come up for auction it would fetch an estimated $5,000,000.00 USD.
William Shakespeare's Autograph.

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