Here is a tutorial that shows you how to make a quick and easy sig with Photoshop CS. The tutorial is meant to be quite easy but the ending sig is decent.
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Make a new image that is 400 x 100 (can be changed to your liking) with a white background.

Reset the default colors to white and black and then go to Filter > Render > Clouds.

Hit ‘CTRL + B’ and mess with the color to find what you like.

Paste an image you like into your sig. You might need to crop it a little.

Move it to its desired location and change the layer type to Luminosity

Select your l***o tool with a 15px mode. Highlight the majority of the picture.

Hit the [ O ] in the layer menu to create a layer mask.

Put the desired text into your sig.

Go to Layer > Layer Style > Blending Options

Check the ‘Drop Shadow’ Box. Tweak it to your desired effect.

Check the ‘Outer Glow’ Box. Tweak it to your desired effect.

Here is the finished design…

Add Brush effects to enhance the sig.

VOILA! You are done.
Hope this helped