A proprietary Bank of America indicator points to 20%-plus gains in the stock market over the next year. Here's what the firm recommends buying now ahead of the rally.

· Bank of America Merrill Lynch's proprietary sell-side indicator showed analysts were less optimistic about the stock market in May. 
· The market went on to gain 20% on a median basis when the indicator was historically at these levels, according to Savita Subramanian, the head of US equity and quantitative strategy.
·...