The trick to a good signature isn't really about making a good edge, or border, but rather bringing proper focus to your topic. For example, you can make a border out of an environment without having to make an actual border. I'll show you what I mean.
In this standard picture, there are no edges used anywhere. However, your attention does not immediately go to the border, being the tree and bush on the left, but rather the more detailed, focused area of the sun, and background. Advanced signature creators usually drop the idea of a border in exchange with a splash of color, or a gradient of light. It's simple, attractive, but will not pull your eye away from the topic. Rather push your eye into taking the time to look at your subject.