supported substitutes are:
$$fullname$$ => name of the user,
$$firstname$$ => first name of the user,
$$lastname$$ => last name of the user,
$$domain$$ => domain name for mail-address,
$$email$$ => email-address of the user,
$$date$$ => todays date,
Note: substitutions are performed, as the signature is added to the email, in EDIT Mode of
the signature in question the above listed placeholders are shown, if used.
Note: this is the discussed feature for signature placeholder substitution of 1.4.
It was never dropped, (as assumed earlier, but not useable, as substitution was performed for almost
every edit of the signature (and the placeholders where lost that way))
