You can see the email, because I only signed it. Signing it verifies that I am who I say I am. NonvocalScream at WMF projects.
Can't you sign it with just a signature? That is, something which goes at the bottom of the email? The line at the top is completely pointless - if I care about whether or not an email is signed, I'll scroll down to the bottom where I would expect to find the signature. A correctly formatted signature can be hidden by most email clients, I believe, then you wouldn't be annoying anyone.