The base of the shield contains a Lamb of God and scallop shells- very Christian symbols, to be expected for a city named after a saint. The ship in the chief refers to the city's location on the ocean, and it's foundation by English settlers (thus the cross of St. George on the flag of the ship).

The supporters are sailors (appropriately), one dressed as one of John Cabot's men, and the other as one of Gilbert's.

There is an official version of this page here.