"Things You Wouldn't Know If We Didn't Blog Intermittently."
Alfred Hitchcock was said to be obsessed with bowels and bowel movements (B.M.). That's why these particular letters are inserted as a kind of an inner joke.
If he engraved the ring with "T.S. from B.M." it sounds like he was having some problems in that area.
The engraving read "TS from BM". After reading a newspaper article at the library, Charlie learns that the TS refers to Thelma Schenley and the BM refers to Thelma's husband Bruce Matthewson. Charlie also learns that Thelma Schenley Matthewson was the third victim of the Merry Widow Murderer
Second anon, that is in fact the relevance to the plot of the movie, but my question asked about the significance NOT related to the plot. The first Anon is correct.
Teresa Wright is the correct spelling of the actress' name -- I know, because it was my maiden name.
Fixed. Thank you, Teresa.