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 Dividend Stocks Itching to Pay You More 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 Stocks Insiders Are Snapping Up 3D Systems ( DDD) This company manufactures & sells 3D content-to-print solutions & 3D printing systems. This stock is trading up 11% at $46.35 in recent trading. Today's Volume: 2.87 million Average Volume: 1.57 million Volume % Change: 217% From a technical perspective, DDD is exploding higher here right off some near-term support at $42 with monster upside volume. This move is quickly pushing DDD within range of triggering a major breakout trade. That trade will hit once DDD manages to take out its 52-week high of $46.92 with high volume. Traders should now look for long-biased trades in DDD once it manages to sustain a move or close above $46.92 with volume that hits near or above 1.57 million shares. If that breakout triggers soon, then DDD will set up to enter new 52-week high territory, which is bullish technical price action. Some possible upside targets are $50 to $60 in the near future. Facebook ( FB) This company operates a social networking website. Millions of people use Facebook everyday to keep up with friends, upload an unlimited number of photos, share links and videos, and learn more about the people they meet. This stock is trading up 7.8% at $25.89 in recent trading.