St. Dunstan's shield carries the bishop's miter to symbolize his service as Archbishop of Canterbury; the scroll to symbolize his devotion to learning; the crown to symbolize his life dedicated to the King and Savior of us all; and the tongs to remind us of his practical vocation as a metallurgist. It may be viewed on the banner in the sanctuary.
St. Dunstan lived  ca. 925 CE - 988 CE*.

An alternative explanation of the crown is that St. Dunstan was advisor to a number of the pre-Norman kings.

* 'CE' is an abbreviation for 'Common Era', and replaces the Christian term 'AD', 'Anno Domini', meaning 'The year of the Lord'.