Saving as a brush works great, but only to manually apply it to the image one at a time. I interpret your question to mean you want to apply a signature to a folder of images in an automated fashion... to do that in photoshop, you might want to check out the following link:
http://www.photosig.com/articles/151...tbn5Npx_5RjN1Z
This gives a good method of creating a separate signature file and creating an action to apply to to a group of images in an automated batch. This method requires using both PS and ImageReady - but works well...
Hope this helps...