In trading on Friday, shares of the SPDR Wells Fargo Preferred Stock ETF ( PSK) entered into oversold territory, changing hands as low as $43.19 per share. We define oversold territory using the Relative Strength Index, or RSI, which is a technical analysis indicator used to measure momentum on a scale of zero to 100. A stock is considered to be oversold if the RSI reading falls below 30.In the case of SPDR Wells Fargo Preferred Stock, the RSI reading has hit 27.2 — by comparison, the RSI reading for the S&P 500 is currently 56.9. A bullish investor could look at PSK's 27.2 reading as a sign that the recent heavy selling is in the process of exhausting itself, and begin to look for entry point opportunities on the buy side. Looking at a chart of one year performance (below), PSK's low point in its 52 week range is $39.12 per share, with $44.96 as the 52 week high point — that compares with a last trade of $43.25. SPDR Wells Fargo Preferred Stock shares are currently trading up about 0.3% on the day.