The Seal of the President of the United States is used to mark correspondence from the U.S. president to the United States Congress, and is also used as a symbol of the presidency. The central design, based on the Great Seal of the United States, is the official coat of arms of the U.S. presidency and also appears on the presidential flag.
The presidential seal developed by custom over a long period before being defined in law, and its early history remains obscure. The use of presidential seals goes back to at least 1850, and probably much earlier. The basic design of today's seal originated with Rutherford B. Hayes, who was the first to use the coat of arms on White House invitations in 1877. The precise design dates from 1945, when President Truman specified it in Executive Order 9646. The only changes since were in 1959 and 1960, which added 49th and 50th stars to the circle following the admissions of Alaska and Hawaii as states. * Wikipedia.