The following tutorial will teach you how to create the sparkle effect like the one on my sig using the basic brushes that come with photoshop.
First, you may need to go grab some brushes at deviantart.com or search google for some to add into photoshop.
Next, create a new document, maybe 400x125 as this is the normal signature size and use your new brushes to brush up the background.
Now reset your brushes and pick a small soft round brush, maybe 5-10 pixels or less. Make sure the foreground color is white and the background color is black.
Now set the scattering options:
Now, brush around your image.
I made random changes to scattering, shape and other dynamics as well so they wouldn't appear to be the same size, etc.
The next step I did to the image was set the change the brightness and color contrast options.
Select the top most layer and click on the create new fill or adjustment layer in the layers tab and select the option color balance.
Make in the color of your choice. After choosing a color, click the create new fill or adjust layer button again but instead of clicking on color balance, select brightness/contrast and use the following settings:
Click ok, the stars should now begin to appear like the ones on my sig.
I suggest you experiment with the size of the brush as it may provide you with a different outcome.
More Tutorials: 
