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.Major moves in volume can signal unusual activity, such as insider buying or selling -- or buying or selling by "superinvestors." >>5 Stocks Set to Soar o Bullish Earnings 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 Poised for Breakouts 3D Systems 3D Systems ( DDD) manufactures and sells 3D content-to-print solutions and 3D printing systems. This stock is trading up 2.7% at $33.11 in recent trading. Today's Volume: 2.97 million Average Volume: 5.27 million Volume % Change: 50% >>4 Hot Stocks to Trade (or Not) From a technical perspective, DDD is bouncing higher here and breaking out above some near-term overhead resistance at $32.35 with decent volume. This move is quickly pushing shares of DDD within range of triggering another near-term breakout trade. That trade will hit if DDD manages to take out some near-term overhead resistance at $34.41 with high volume. Traders should now look for long-biased trades in DDD as long as it's trending above $32.35 and then once it sustains a move or close above $34.41 with volume that hits near or above 5.27 million shares. If that breakout hits soon, then DDD will set up to re-test or possibly take out its next major overhead resistance levels at its 50-day of $37.33 to $37.85. eBay eBay ( EBAY), a global commerce platform and payments provider, is trading up 3.7% at $56.26 in recent trading.