The Relationship Between the Stock Market and Forex Marketsby Kathy Lien
The equity market can impact the currency market in many different ways. For example, if a strong stock market rally happens in the U.S., with the Dow and the Nasdaq registering impressive gains, we are likely to see a large influx of foreign money into the U.S., as international investors rush in to join the party. This influx of money would be very positive for the U.S. dollar, because in order to participate in the equity market rally, foreign investors would have to sell their own domestic currency and purchase U.S. dollars. The opposite also holds true: if the stock market in the U.S. is doing poorly, foreign investors will most likely rush to sell their U.S. equity holdings and then reconvert the U.S. dollars into their domestic currency - which would have a substantially negative impact on the greenback. This logic can be applied to all the other currencies and equity markets around the world. It is also the most basic usage of equity market flows to trade FX.
Source: http://www.investopedia.com/articles/forex/05/MA.asp; http://www.gftforex.com/; http://www.bktraderfx.com/site/members-benefits