When I make a signature for someone I usually convert a VQA video to AVI (using XCC Mixer), then I use Camtasia Studio (which can be downloaded from
www.techsmith.com) or ImageReady or a combination of both to convert the AVI to an animated gif, add some fancy effects, crop the image and add in the name of the person I'm making the signature for.
In the past I mostly used Camtasia Studio, but I started using ImageReady more now and now I only use Camtasia Studio when I'm unable to convert the AVI to an animated gif with ImageRead (the reason why it won't work probably has something to do with the codecs).
I hope this helps you out.