Horizontal marquee on the top and bottom each w/ about a 6 pixel stroke... Possibly a 1-2 pixel border w/ the vertical marquee tool.
I select a box the same width as the sig, and 10 px less than the height. Then center it both ways, invert the selection and fill with your color. Thats how I do mine.
Select tool. Go over the top with the desired size. Fill on new layer. Duplicate layer, vertical flip.
Or you could use the line tool... and hold ALT (I think it is) and it makes your lines straight. Easiest, most versatile IMO. You could do CTRL/ALT Edit>Stroke.. but