HSBC's technical-analysis team has thrown up the ultimate warning signal. In a note to clients released Wednesday, Murray Gunn, the head of technical analysis for HSBC, said he had become on "RED ALERT" for an imminent sell-off in stocks given the price action over the past few weeks. Gunn uses a type of technical analysis called the Elliott Wave Principle, which tracks alternating patterns in the stock market to discern investors' behavior and possible next moves. In late September, Gunn said the stock market's moves looked eerily similar to those just before the 1987 stock market crash. Citi's Tom Fitzpatrick...