Portal 2 - Co-op Gesture Test Issues
I'm not sure what the red circle would indicate, but it took me a minute to figure out that holding down the gesture key opens a radial menu with icons around the perimeter. (It took a minute at first because there's only one icon at the beginning... not much of a circle) Moving the mouse towards the icon (in this case, up) while holding the key down and then letting go of the gesture key executes the gesture.