The death cross is a technical indicator that occurs when the 50-day moving average moves below the 200-day moving average, signaling a potential downward trend for the stock. This bearish sign has appeared on United Rentals' chart, which could lead to a decline in the stock price in the short term. However, it's important to note that seasoned investors don't blindly trade death crosses and consider other factors like price levels and company fundamentals before making decisions.