Make a new layer(layer 1), and press ctrl+shift+alt+e. This fills the layer up with an image of how your sig looks now.
Then create a layer under this layer(layer 2) with the splatter brush, and do whatever you want to.
Then select layer 1, and make it a clipping mask. Press ctrl+t and start moving it around until you're satisfied with the result.
When you're done, press enter.
Too lazy to make screenies right now, so you'll have to make do with a text-based explanation.
