I upgraded my OS to Kubuntu Hardy last april, and now I noticed that Kmail can put signature above reply quotes.
To do this, open Kmail/Kontact, and click:
click on “Composer” on the left menu, and you will see option “Insert signatures above quoted text”. check this option.
And you can put your signature in Kmail by choosing “Identities” on the left menu, and click “modify” button on the right.
click “enable Signature” and you can type in your signature there. Pretty easy!