How many times have you been asked this question?
Recently, I was asked by a 6th form student from West Africa. I repeated for the nth time my standard answer; "Sincerely is when you know the recepient's name. Faithfully is when you start your formal letter with Dear Sir/Madam"
I added my not-very-useful way of remembering it "You cannot write SIR and SINCERELY in the same letter" Does anyone know a better mnemonic?
Anyway, this African boy responded unexpectedly; "In Africa we use Yours Faithfully in a polite formal letter and Yours Sincerely in an angry complaining letter."
I didn't know that. I found it interesting. I can imagine this confusion resulting in a lot of tribal/colonial lashes in the past!