It's the open secret that nobody in government wants to talk about: That cherished presidential signature that's tucked away in a scrapbook or framed for all to see might never have passed under the president's hand.

For decades, presidents of both parties have let an autopen do some of the heavy lifting when it comes to scrawling their signatures. The machine was recently put to use signing a bill into law, apparently a first.

Overseas and out of reach when lawmakers passed an extension of certain provisions of the Patriot Act, President Barack Obama employed the autopen to sign it, a step the White House has been mum about ever since.

"I always heard the autopen was the second most guarded thing in the White House after the president," says Jack Shock, who had permission to wield former President Bill Clinton's autopen as his director of presidential letters and messages.

Jim Cicconi, who oversaw the use of autopens for President George H.W. Bush, recalls that the plastic signature templates for the machines — yes, there was more than one autopen — would wear out from repeated use.

Ronald Reagan had 22 different signature templates, including "Ron," "Dutch" and other iterations, to boost the aura of authenticity surrounding his fake signatures, says Stephen Koschal, an autograph authenticator who two years ago published a guide to presidential autopen signatures.

It's not just ordinary Americans who get the autopen treatment.

Koschal says he once visited Vice President Dan Quayle's office in the Capitol and spotted a signed photograph from the first President Bush that he said had clearly been autopenned.

Obama took the presidential autopen out of the closet and into a new realm.

While traveling in Europe last month, Obama directed his staff in Washington to use an autopen to sign into law an extension of certain Patriot Act powers to fight terrorism. The legislation had been approved by Congress at the last minute, and there was no time to fly it to France for Obama's signature before the anti-terrorism powers expired.

It was believed to be the first time a president has used an autopen to sign legislation. Autopen signatures generally are reserved for more personalized correspondence that doesn't score a real signature, say officials from administrations past.

(Read by Lee Hannon. Lee Hannon is a journalist at the China Daily Website.)