How did John's name become associated with the sisters?

The parish church in the town of Angri, Italy where the Sisters of St. John the Baptist originated  was dedicated to St. John the Baptist.  The people of Angri had a great devotion to their patronal saint.  When Fr. Alfonso Maria Fusco, a native of Angri and the founder of the Baptistines,  sought approval for his new community, the local bishop instructed Fr. Fusco to place the small community under the name and patronage of St. John the Baptist. 

As a result, the Feast of the Nativity of St. John the Baptist on June 24 as well as the Feast of John's Martyrdom (Beheading) on August 29 are  patronal feasts of the Sisters of St. John the Baptist. They are prayerfully prepared for, observed  with great solemnity and celebrated with traditional festivities in all Baptistine convents throughout the world.