INVESTING: Weak markets could lead to a nasty surprise
If you open an account at a brokerage firm and deposit $100, you can sign a margin agreement and borrow enough money from that broker to buy $200 worth of stock. For years, market watchers analyzed the margin interest on the New York Stock Exchange-which measures how much stock people are buying using margin-as a reliable indicator of overbought or oversold conditions. Things have changed today, though, and that could have a serious effect on your portfolio. NYSE margin information…