signed mail + steganography = ?

[baumbach@atmel.com (Peter Baumbach)]

What if you couldn't tell when a letter was signed unless you new the  
public key of the person signing it?  How could this be done?  Encode 
the digital signature with steganography.  Is this possible when  
steganography alters the very message you wish to sign?  I don't know. 
  
The benefit of this is signed and unsigned messages look like each other. 
People can't be lazy anymore and just assume the signature is yours.  
Your boss isn't likely going to notice you used pgp to sign your mail. 
  
Peter Baumbach
baumbach@atmel.com