First off, pick a sig that look nice, I'll use my current one.

Then make a new layer, and set it to soft light.

Now pick a color that you want to blend with your sig and pick a grunge brush and brush around.

I already had a boarder and text added. You can take the time and add that yourself unless you already have it added.

feel free to add more layers and use differt effects to make your sig look different and original.

Final