Anthony Davidow, portfolio strategist at Guggenheim Investments, which manages the Currencyshares ETFs, says he thinks China's currency has upside potential. "The basic premise is it's undervalued," thanks to China's efforts to keep its exports growing, "and China will have to be part of any sort of global recovery."

In addition to single-currency ETFs, there are also ETFs representing a basket of currencies. For investors who don't want to construct their own currency basket using ETFs, or monitor an array of single-currency ETFs, these may make more sense.

Consider currency-basket ETFs composed of emerging-market currencies or of currencies from commodity exporting countries to express a bullish outlook. Several firms offer this type of ETF.

Another way to take a bullish view on the economy is to take a bearish view on currencies that investors normally use to take cover from economic storms: the dollar ,the yen and to a lesser extent the Swiss franc . PowerShares DB U.S. Dollar Index Bearish Trust performs like a futures index based on a short position on the U.S. dollar index.

However you decide to take a position, experts agree that it’s important to consider currencies when constructing your portfolio.

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