The autopen machine, a modern duplicating device, was developed in the 1930s. Appealing because it leaves a mark less impersonal than a stamp or copy of a signature, the autopen produces a duplicate signature that is almost impossible to distinguish from the original. However experts can recognize an autopen signature because it is applied using an even pressure, while an individual applies uneven pressure to the pen.
President Truman may have been the first President to use the autopen for correspondence. Although President George W. Bush sought a legal opinion from the Justice Department, which rules that it was legal to use, President Obama was the first President to use the autopen to sign legislation.