And then theres always paint!
Anyways very simple low down:
First of all you need a canvas! Just whatever space you wanna work with:
Lots of peoeple like to use 400 x 100 pixels, but it doesn't really matter.
Next make a pretty background using various tools like the paint bucket, brushes, pen tool etc

(ver quick example, I just use the pen tool and made some shapes)
Then you get yourself a render, from somewhere like planetrenders.net which just means a picture of something.
http://planetrenders.net/renders/dis....php?pos=-6125
^I used that one
Copy and paste it on you bg, add some text with a text box (like fancy text on word) and a border (select it all, right click and select stroke)
and tada! you have a signature! (although a very simple one)
Thats it really, then you just mess around with all the various settings as you get used to the software you're using.