Arb (gesture)

Arb, short for arbitrage, is a system of hand signals used to communicate buy and sell information in an open outcry trading environment. The system is used at many financial exchanges, such as the Chicago Mercantile Exchange.

Traders usually flash the signals quickly across a room to make a sale or a purchase. Signals that occur with palms facing out and hands away from the body are an indication the gesturer wishes to sell. When traders face their palms in and hold their hands up, they are gesturing to buy.

Numbers one through five are gestured on one hand, and six through ten are gestured in the same way only held sideways at a 90 degree angle (index finger out sideways is six, two fingers is seven, etc.). Numbers gestured from the forehead are blocks of ten.

These rules may vary among exchanges or even among floors within the same exchange; however, the purpose of the gestures remains the same.