#5匯控發出盈利警告之前有沒有市過，是否代表全球的經濟轉差？請分析

No, it only means that HSBC had made a big loss in the US mortgage market.
Actually a lot of US big corporations tends to give profit warnings in October (US financial year is same as calender year), this is to lower the customer expectation and to avoid a slump in share price when the actual profit is announced. That's why October is the share price drop month.