The signature of a renowned author can greatly increase the value of a book. However, books aren’t the only things authors sign—their signatures can also be found on legal documents, letters, and other types of manuscripts. Some signatures are rarer than others, of course, and in general, the more scarce the signature, the higher its value. The John Hancocks of the following authors are particularly prized.

1. HARPER LEE

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Reclusive author Harper Lee seldom signed her books, so a signed first edition of To Kill a Mockingbird in good condition can be worth at least $20,000. In 2015 Lee’s publishers released 500 special leather-bound signed editions of Lee’s second book, Go Set a Watchman, for $1500, no doubt hoping that those books would also become highly collectable. Indeed, Lee signed far fewer copies of Watchman than Mockingbird before her death, so it is possible signed editions of Watchman will eventually become even more sought-after.

2. WILLIAM SHAKESPEARE

Five of Shakespeare's signatures. Image credit: Getty Images

Today there are only six known copies of Shakespeare’s signature, which makes his autograph hot property. All of the signatures are featured on legal documents, with three of the six from copies of the celebrated playwright’s will. Scholars are especially fascinated by Shakespeare’s signature in part because it was so messy, and he seemed to spell his famous name in a number of ways, from Shackper to Shackspere. Because of its scarcity, it is thought to be the most valuable author signature in the world. Were a Shakespeare signature to come onto the market today (extremely unlikely, since all the existing signatures are held by institutions), it’s estimated that it would fetch at least $5 million, and were one to be discovered on a play or poem written by his own hand, it might be practically priceless.

3. JAMES JOYCE

An early edition of Ulysses. Image credit: Getty Images.

Because James Joyce's Ulysses was banned in both the UK and America for its racy content, first editions of the book have become one of the most sought-after 20th century tomes, making a signed first edition a bit like gold dust. A super-rare signed first-edition of Ulysses in mint condition—the only part that had been read was the last section, with all the naughty bits—sold at auction in 2009 for £275,000 ($398,000 U.S). Joyce’s signed letters are also impressively valuable; in August 2015, two of them fetched $25,000 at auction.

4. F. SCOTT FITZGERALD

Signatures by F. Scott Fitzgerald are fairly rare, in part because at the time of his greatest success, after The Great Gatsby was published, he was living in Paris and was relatively inaccessible to autograph hunters. Letters signed by Fitzgerald are particularly sought-after, and because institutions and libraries are especially keen to archive his letters, the prices are often pushed up—in 2004, one letter came up for auction and fetched $90,000. A first edition of The Great Gatsby, inscribed by Fitzgerald himself to Harold Goldman (who Fitzgerald calls “the original Gatsby"), was auctioned in 2015 and went for an impressive $191,000.

5. J. D. SALINGER

J.D. Salinger became reclusive in the 1950s, rarely replying to fan letters or engaging with the public, making his signature extremely rare. When he did sign books, he often inscribed a message alongside his signature. Today, the inclusion of a message is one of the ways dealers discern whether a Salinger signature is genuine. A batch of 41 typed and signed letters from Salinger to a girl named Christine, which comprised over a decade’s worth of correspondence, was auctioned in 2014 for $185,000.

6. ERNEST HEMINGWAY

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Hemingway’s signed letters, especially those to his celebrity friends, are a good investment—a fond note he typed to his great friend Marlene Dietrich in 1955 sold for $35,000 in 2014, and a handwritten missive to Ezra Pound in 1925 netted $157,326 when it was sold in 2007. Signed Hemingway books can be even more valuable—a first edition copy of his most celebrated work, For Whom the Bell Tolls, inscribed to his wife, Martha Gellhorn, sold in 2004 for $310,400, and a very rare early edition of his 1926 book The Sun Also Rises was sold at auction for $366,400.

7. CHARLOTTE BRONTË

Charlotte Brontë’s signature rarely comes onto the market, but when it does it most often comes in the form of her letters. In 2009 a letter refusing a proposal of marriage from Reverend Henry Nussey went up for auction and sold for $56,250, despite the signature having been cut away and later restored. In 2013 a tiny signed handwritten poem Brontë composed in 1829, when she was just 13, was auctioned for £92,450 (about $134,000). However, items such as these are extremely rare, with only two similar items appearing on the market in the last 40 years.

8. CHARLES DICKENS

An inscription by Dickens on The Pickwick Papers, from 1839. Image credit: Getty Images

Charles Dickens generally signed his name with a blue fountain pen, making forgeries easier to spot. In 2014 a signed copy of Dickens’s best-selling book A Tale of Two Cities, inscribed to his fellow author Mary Ann Evans (otherwise known as George Eliot), was sold for an astonishing £275,000 (about $398,000). Letters written or signed by Dickens are also valuable—a simple handwritten note can go for about $4,000 to $7,000.

9. GEORGE ORWELL

Sometimes, although an author’s signature is valuable, there is a particular book that makes that signature even more valuable. George Orwell’s signature is very collectable, with letters going for around $10,000, but signed copies of his most celebrated novel—Nineteen Eighty-Four—are so rare they are exceedingly valuable. When the novel was published in 1949, Orwell was already extremely ill, and he died not long afterward. He therefore signed very few copies of the book; despite this, one recently came onto the market and was snapped up for $26,500.

10. J. K. ROWLING

A page from the copy of The Tales of Beedle the Bard that was sold at auction in 2007. Image credit: Getty Images

The print run for the first edition of Harry Potter and the Philosopher’s Stone published in the UK (it was renamed Harry Potter and the Sorcerer’s Stone for the US release) included only about 2000 copies, and of those, only about 500 were hardback. Most of these first editions were sent to libraries, and so very few survive in good condition. This has meant that a signed first edition of Rowling’s first book is now worth about $24,000.

In 2007, a handwritten copy of The Tales of Beedle the Bard was sold at auction—Rowling handwrote just seven copies of this book, intending it never to be published. Six copies were gifted to people closely connected to the Harry Potter franchise and the seventh was auctioned for charity, where it was acquired by Amazon for an astonishing $3.98 million.