It is basically, when you look at a signature, or image, the point where your eyes look near immediately, if they look at some area in it where there is pretty much nothing, then there isn't much of a vocal point, when making a signature or other graphics, you must try and set a fixed vocal point in order to draw the spectator in to your graphic, for example, some people may create a sort of fire effect behind the render, or area in which you want a focal point, essentially creating a halo effect circling a fixed point and creating a focal point.
Sorry for the long response xD