Minus Tick

Minus ticks are important because not only do they indicate the price trend of a stock, they also trigger restrictions on short sales. In the United States, when a stock is on a minus tick, traders are generally prohibited from shorting the stock. This rule (called the short sale rule or the tick test) exists to prevent traders from jumping on the bandwagon to destabilize a stock's price (note that exchange-traded funds can be shorted on a minus tick, however).