When writing , the symbol for the American dollar is the dollar sign ( $ ) . The exchange rate between the Hong Kong dollar and the United States dollar has also been linked since 1983 at HK$ 7.8 \/ USD , and pataca of Macau , pegged to Hong Kong dollar at MOP1 .03 \/ HKD , indirectly linked to the U.S. dollar at roughly MOP8\/USD . Several oil-producing Arab countries on the Persian Gulf , including Saudi Arabia , peg their currencies to the dollar , since the dollar is the currency used in the international oil trade .