Hand signaling, also known as arb or arbing (short for arbitrage), is a system of hand signals used on financial trading floors to communicate buy and sell information in an open outcry trading environment. The system is used at financial exchanges such as the Chicago Mercantile Exchange (CME) and the American Stock Exchange (AMEX). The AMEX is the only U.S. stock market to permit the transmission of buy and sell orders through hand signals.