var overlay = Overlays.addOverlay("cube", {
    position: Vec3.sum(MyAvatar.position, Vec3.multiplyQbyV(MyAvatar.orientation, { x: 0, y: 0, z: -3 })),
    rotation: MyAvatar.orientation,
    dimensions: { x: 0.3, y: 0.3, z: 0.3 },
    solid: true
  });
  print("My overlay: " + overlay);
  
  Overlays.mousePressOnOverlay.connect(function(overlayID, event) {
    if (overlayID === overlay) {
        print("Clicked on my overlay");
    }
  });