TV
Here’s a viewer’s letter. It comes from Mrs. Margaret Forsdyke: “Since watching your program, I have become a new person. Yours sincerely, Mr. Arthur Vickers.”
— Michael ‧ Do Not Adjust Your Set

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The letter claims that watching the programme has made its writer a new person. A different name at the end gives that familiar praise an unexpectedly literal meaning. The mismatch between the introduction and signature supplies the joke without any further explanation.
Context reviewed