[Evolution] possibly stupid PGP/GPG display question

[Mike Earl <mike earl rcn com>]

I have a worry about the way the GPG signatures are displayed when
reading mail in evolution.  Is there anything to prevent somebody from
just sending a HTML message with that horizontal line, "This message is
digitally signed", icon (etc.) in place of a .sig?  And would this be
obviously different from a signed message other than by viewing source?