If your UA software is configured to automatically include cash series with all futures contracts (through the "Optional Fields" tab of portfolio settings or the Cash/Saturdays screen of UA Preferences), then you can use this feature to toggle the cash prices on and off your UA charts.
If the cash is displayed and you want to remove it, right click your mouse to bring up this menu, then click "Display Cash." The chart will be redrawn without the cash. Repeat the procedure to return the cash to the screen.