Someone asked the question on Stack Overflow on how to create a signature box using actionscript 3 so I decided it was a good excuse to demo one in the playground. I saved the .fla back as far as I could (it's in a CS4 version). Also, I've published this for Flash Player 9 in hopes that all can see.
As usual, you'll find the source at the bottom. Feel free to tear it apart and let me know if you have any questions.