WINDERMERE, Fla. ( Stockpickr) -- Professional traders running mutual funds and hedge funds don't just look at a stock's price moves; they also track big changes in volume activity. Often when above-average volume moves into an equity, it precedes a large spike in volatility.>>5 Big Stock Charts You Need to See Major moves in volume can signal unusual activity, such as insider buying or selling -- or buying or selling by "superinvestors." Unusual volume can also be a major signal that hedge funds and momentum traders are piling into a stock ahead of a catalyst. These types of traders like to get in well before a large spike, so it's always a smart move to monitor unusual volume. That said, remember to combine trend and price action with unusual volume. Put them all together to help you decipher the next big trend for any stock. With that in mind, let's take a look at several stocks rising on unusual volume today. >>5 Huge Trades for a Volatile 2013 PDF Solutions ( PDFS) This company provides infrastructure technologies and services to improve yield and optimize performance of integrated circuits. This stock is trading up 5.4% at $15.21 in recent trading. Today's Volume: 213,000 Average Volume: 117,854 Volume % Change: 217% From a technical perspective, PDFS is ripping higher here right off its 50-day moving average of $14.08 with above-average volume. This move is starting to push shares of PDFS into breakout territory, since the stock has cleared some near-term overhead resistance levels at $14.79 to $14.95. Shares of PDFS are now trading in new 52-week high territory, which is bullish technical price action. Traders should now look for long-biased trades in PDFS as long as it's trending above its 50-day at $14.08, and then once it sustains a move or close above those breakout levels with volume that hits near or above 117,854 shares. If PDFS can maintain this trend, then this stock has a great chance of tagging $18 to $20 in the near future. GeoEye ( GEOY) This company is a provider of imagery, imagery information products and image processing services. This stock is trading up 7.2% at $36.46 in recent trading.