Here's an easy way to convert a black and white signature scan or illustration into a layer masked graphic which you can then recolor and use on any background. The trick is that the image is its own mask.
- Open your image in Photoshop. Apply Sharpening and Curves if needed.
- Add a new Layer Mask. With the layer mask selected, select Image > Apply Image. In the dialog box, use these options: Source: (your file name), Layer: Merged, Channel: Gray with Invert checked, Blending: Normal with 100% Opacity and click OK.
Signature is Joan of Arc's from wikipedia commons