1. An ultrasonic diagnostic image display comprising: a first two dimensional image having an image plane orientation in relation to a transducer; a second two dimensional image having a plane orientation relative to the plane of the first two dimensional image; and a plane orientation icon, displayed on a display screen concurrently with the first and second images, which depicts the relative angular planar orientation of the first and second images, wherein the icon comprises a depiction of at least one of the image planes as seen from a common reference as the plane of one of the images is tilted relative to the other