Fake denominations of United States currency have been created by individuals as practical jokes, by money artists such as J. S. G. Boggs, or as genuine attempts at counterfeiting. Before the passage of the National Banking Act of 1863, individual banks in the United States were permitted to issue their own currency. Many banks did so, resulting in a proliferation of banknotes of various denominations, and the need for merchants to have books explaining the characteristics of various notes. Several people have produced $0 bills as a joke, with pictures of Barack Obama, George W. Bush and other people. The bills usually say "ZERO DOLLARS" in big letters.