Automatically adding text to comment after comment is submitted

[mike159]

I am using WordPress for my site. The thing I am trying to do is automatically add text to a comment after it has been submitted by the commentator. Kind of like a signature. What I want is to have the comment field look normal when someone is posting, and have the text area where the comment is typed to be empty at first. Then after they post the comment, a block of text would be automatically added a paragraph or two below their comment, but in their comment area. If that makes sense. So have the comment field empty when someone is typing, and after they submit their comment, a block of text gets added a line or two below their comment text, but still in the same comment. How can I do that?