A bear market may last for a week, a month or even a few years, but it can take only a day, an hour or even a few minutes for the value of an investment portfolio to be slashed to half of its former value. Some bear markets start with a bang, like the crash of ?7, others creep up slowly so that investors do not realise they are in a bear market and carry on as if nothing has happened. Of course, not even the experts can accurately forecast what the market will do. However, there are signs that...