It is the letter A which stands for Adultery in the book.
Hester Prynne had to wear the Scarlett Letter because she was an Adulterer Adulteress. her Husband left and she got pregnant while he was gone.
The Scarlet Letter "A" represents the act of adultery.
able -- aide. aloe, also, alms, aura, awry, alas, ajar ally akin, aged, agog, acre, arms, arid, army, atop, area, ally, apex.
i don't know if this is what you mean but there is babu and batu