Gradient Maps are a good way of adding depth and colour into a signature.
View the image below, this is one of my famous sigs without a gradient map;
Now below is it with a gradient map;
How to:
Navigate yourself to this button;
Click on it and you'll be left with this menu, choose Gradient map;
You'll now be presented with a Gradient Map editor menu, this is simple to use;
Adjusting the colours in the slider changes the effect it has on the Signature, below are the colours I used;
Accept the settings and you should be left with an image looking similar to this;
Change the layer setting to 'Soft Light' and your signature should have a lot more depth and colour.
Creditz for tutorial to LiteVoid