Citi outlined its playbook for navigating the market amid fears of a stock bubble. Investors should stay long US stocks until the bubble bursts, strategists wrote in a client note. The bank said it was monitoring two indicators that could signal when the market is starting to turn. If you're fretting over a bubble, don't sell your stocks just yet. That's the takeaway from the latest Citi research, which outlined the bank's ideal investing playbook as the stock rally continues and valuations get fr ...