The story
In reference to Susan B. Anthony (1820–1906), a women's rights activist whose portrait is featured on the coin's obverse. Further etymology In her youth, Susan Anthony and her sisters responded to a “great craze for middle initials” by adding middle initials to their own names. Anthony adopted “B.” as her middle initial because her namesake Aunt Susan had married a man named Brownell. Anthony never used the name Brownell herself, and did not like it.
Etymology from Wiktionary, CC BY-SA 4.0.