1. Make a new document, i made one 325*120
Fill it with black.

2 Start brushing, press "d" to restart colors and then "x" for conver foreground colour into backround color and vice versa.
Go crazy! use abtract brushes.
Your sig should look like this

Make a new layer, press "x" and brush again.
You should have something like this

3. Apply Brightness/Contrast Layer > New adjustment layer > Brightness/Contrast
With this settings

Make a new color balance Layer > New adjustment layer > Color Balance
And apply this settings



You should have this beautiful color :P
Now apply another color balance

With this settings



Keep the color balance layer selected and add clouds
You should have something like this

Make another color balance with this settings:
Midtones: -74 0 0
Shadow: -61 0 0
Hightones: -67 0 53
Keep the color balance selected too and add clouds.
Add difference clouds
You should have this beautiful multicolor effect
4. Lets make a border, press ctrl and select the first layer
You should got a selection
Make a new layer, on the top, and add stroke, Edit > Stroke

Use the eyedropper tool to take a color of the sig.

And add more stroke


Final Result














More Photoshop: