Well photoshop is generally but always a raster based program. The other big design program in Adobe, Illustrator works with Vector graphics. Vector graphics are 100% scalable due to the shapes being mathematically defined at any size.
Raster Images are made up of any amount of pixels and are much simpler but have the tendency to get pixelated.
Really all I would suggest for you fudpex would be to just up the size of your sig to a higher resolution, that should take care of the fuzzyness...