What about using XML Signature ( http://www.w3.org/TR/xmldsig-core )? This standard can be used not only to prove who is sending a message, but also that the contents message have not been altered by a third party during transmission, which is another common security concern not mentioned in this
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
Thanks to adu on #vos for the original inspiration:
http://img89.imageshack.us/img89/2124/vos5ur.png
- From that concept, I did a couple of iterations of increasing the text
size:
http://interreality.org/~tetron/vos%20adu%20logo%20mine.png