As directed by the U.S. Constitution, the president of the United States generally signs federal legislation into law. His signature is not required when Congress overrides a presidential veto or when he declines to act on legislation, in which case a bill automatically becomes law, explains Cornell University Law School.
Presidents have long used multiple pens to sign bills into law, reports National Public Radio. They give these pens as gifts to members of Congress and others who support legislation they sign. President Harry Truman was the first president to keep a box of commemorative pens in his office for signing legislation.