here's where the ASA sent me :
http://www.copyadvice...ims-on-Envelopes.aspx
here's where the relevant pdf is...
http://www.copyadvice...ims-on-Envelopes.aspx
and here's the relevant part of the pdf...
3. Envelopes that Masquerade as Official Correspondence
3.1 Direct marketers should not state or imply on envelopes that mailings are from an official source when this is not the case;
3.2 Claims on envelopes such as “Final Reminder”, “Security Tabbed Documents Enclosed” and “Penalty Notice Enclosed”, are likely to mislead as to the importance and status of the content of mailings and be unacceptable.
I don't think your aunt has much of a complaint, sorry :(