In perhaps the most chilling section, the National Archives has put out the marriage license of Adolf Hitler signed on April 29, 1945 as the German dictator and Eva Braun eloped one day before they committed suicide.
The license, seized by US troops, testifies that Hitler and his longtime girlfriend were "of pure Aryan descent" and asks Braun, "Are you willing to take Our Fuehrer Adolf Hitler as your husband?"
Hitler signs with a scrunched scribble and Braun begins to write "Eva B-" before crossing out the "B" of her maiden name and writing Eva Hitler. The dictator's confidants Joseph Goebbels and Martin Bormann signed as witnesses.
"Signatures tell us a lot about their owners and the circumstances under which they were made," said David Ferriero, archivist of the United States.
The exhibition's signatures show Civil War president Abraham Lincoln to be "decisive," anti-slavery activist Harriet Tubman as "determined" and Hollywood legend Katharine Hepburn as "fearless," he said.
The exhibition highlights the unexpected turns and what-ifs of history. A 1989 card signed by Saddam Hussein thanks new US president George H. W. Bush for his "kind greetings"; two years later, the United States would attack Iraq after Saddam's invasion of Kuwait.
Another display shows the young Richard Nixon's application to be an FBI agent. The fresh law school graduate never heard back -- apparently, he was told years later, due to budget cuts in Washington -- and he returned to California, soon embarking on a political career that would lead him to the White House.
Jennifer Johnson, the exhibition's curator, said that the one historical figure she felt obliged to include was the US revolutionary John Hancock, whose signature is on display in a document as governor of Massachusetts.
Hancock's conspicuously large signature on the 1776 Declaration of Independence from Britain -- on permanent display elsewhere at the National Archives in central Washington -- was so famous that his name has become synonymous with an autograph in American English.
Shifting to the contemporary era, the exhibition demonstrates an autopen. Barack Obama has become the first president to use an autopen, authorizing his signature remotely on urgent legislation when he is away from Washington, triggering protests by lawmakers from the rival Republican Party.
Beyond politics, signatures are increasingly uncommon in the Internet era. US teachers generally emphasize penmanship less than educators in Asian and European nations.
Johnson said she expected children at the exhibition to have trouble reading cursive writing.
"We're certainly ticking that way in how we sign things. When I think about it, I don't put pen to paper that often when making a transaction," she said. "As a historian, I'm terribly sad about it... but I think it's inevitable."