When my husband wrote a business letter and he was disagreeing about something, or making a point, the letter was signed Cordially. That was his way of saying Feck YOU! It has become a standing joke between us. Sincerely was saved for "nice" letters.I was taught the opposite.
If you know the name it is Sincerely.
If you don't it is Faithfully.
The way I remember which is which is if your letter is addressed to Dear Mr Smith - it is Sincerely.
If you don't know who the Feck they are - it is Faithfully.
Addressing royals ia whole nother ballgame though.
---
..
me too. There were plates smashing as well. Has to be a spoof.