NEW YORK (CNNMoney) -- Another trading day and another low for Bank of America's stock. Shares of Bank of America dropped more than 3% Tuesday, hitting a new 52-week low of $5.03 -- its lowest level since March 12, 2009. After the close of trading Tuesday, Bank of America was one of 37 financial institutions downgraded by S&P. Beyond the S&P downgrade, trading could become even more complicated in Bank of America's stock, if it falls below $5. Under that threshold, many broker-dealers will not allow investors to buy or short a stock on margin, according to a spokesperson for...