If you'd like to make sure that the video stream is not viewable, you will need to remove the camera's power. Of course, you'll need to remember to plug the camera back in before you leave it's location. Before turning the power off, be sure to update your firmware to the latest version (3.1.60 or later). This is necessary because some older versions of the firmware (3.1.29 and 3.1.33) had an issue that could prevent reconnection after a power cycle.
If your goal in turning the camera off is to prevent alerts from being triggered and recorded, you can turn off motion and noise detection from within the app. Blue detection buttons indicate that alerts are "On". Grey detection buttons indicate that alerts are "Off". All cameras on the same network within an account are grouped in a way that using the noise or motion alert buttons from the "My Cameras" screen allows you to turn all of the grouped camera alerts on or off. This is useful for turning on alerts for all of your home cameras when you leave for work in the morning and then turning them off when you return in the evening.