The symbol that looks like a Y-shape is representative of a pallium, (pall). This is an ecclesiastical vestment given to St Augustine by Pope Gregory. The cross above the pall indicates he was an Archbishop. Not all coat of arms show the cross. The larger cross may simply be dividing the coat of arms.
The right side of the shield includes a Lily. This represents the month of Mary, (May) and is the month St Augustine died.
In its purest form, the pallium (with cross) is gold, the larger cross and the lily silver, and the background black.
St Augustine, (not to be confused with Augustine of Hippo) was appointed by Pope Gregory the Great to travel to Britannia to convert the “Angles”. Augustine set off with forty fellow monks. They had gone only a short distance when they were overcome with fear at the prospect of facing a barbarous, fierce and pagan nation whose language they did not understand. Augustine was sent back to Rome to persuade the Pope to allow them to return. Gregory refused, but sent Augustine back with letters of encouragement. On arriving in Kent, the group were received by King Ethelbert whose wife Bertha was already a Christian. Ethelbert allowed the brothers to remain. Upon his conversion, the king gave the brothers a residence in Canterbury (his capital). There followed mass conversions. In 602 Augustine, with the king’s help, repaired a church which he dedicated to the Apostles Peter and Paul. This church is known today as Canterbury Cathedral which is the centre of the Anglican communion to this day.
There are some records of Gregory’s correspondence with Augustine. In one letter he says that he has been reflecting of the pagan’s temples. He says that they are “on no account to be destroyed”, but are to be purified so that “the people, seeing that their temples are not destroyed, may abandon their error, and, flocking more readily to their accustomed resorts, may come to know and adore the true God.” Hearing that Augustine had performed miracles, Gregory urges him to remain humble understanding that the miracles are not of his own doing, but God working through him.
St Augustine was presented with various church items in 601, including the pallium, appointing him with the status of Archbishop in the Holy See. Various topics were raised with Rome regarding the church in Britain and Gaul, such as baptism, and marriage. There was caution by other areas in England such as Wales, however Augustine’s example influenced the great missionary efforts of the Anglo-Saxon Church.