Coat of arms of the U.S. Archbishop Thomas Andrew Donnellan, Archbishop of Atlanta (1968–1987). 
The entire "achievement," or coat of arms as it is generally called, is composed of the shield with its charges, the motto and the external ornaments. As one looks at the shield the terms dexter (right) and sinister (left) must be understood contrariwise, as the shield was worn on the arm in medieval days and these terms were used in the relationship of the one bearing the shield.
The dexter impalement is given in ecclesiastical heraldry to the arms of jurisdiction; in this instance, the arms of the Archdiocese of Atlanta.
Atlanta known as the "Crossroads of the South," because of converging railroads which gave the city its early prominence, received its name as the eastern terminus of the Western and Atlantic Railroad which connected north Georgia with the Tennessee River. Originally called Whitehall, then Terminus, and afterwards in 1843 Marthasville, the state legislature finally acquiesced to the wishes of the railroad and accepted the name of Atlanta in 1847, thus naming the city indirectly after the Atlantic Ocean.
The Atlantic Ocean is represented on the shield of the archdiocese by white and blue wavy bars, the heraldic equivalent of the waves of the sea; seven bars in number to symbolize the Seven Sacraments.
The crown of Christ the King denotes the title of the cathedral church, the Eternal King whose redeeming Sacrifice on the Cross is renewed daily in the Holy Sacrifice of the Mass. Above the crown is placed the Cherokee rose, the State flower of Georgia (Rosa Laevigata), as befits an archdiocese located in the Capital City. The Cherokee rose is a white flower with a yellow center.
The crown of Christ the King, in the arms of the Archdiocese of Atlanta, also has the secondary representation of the crown of King George II of England after whom Georgia was named. The blue and white wavy bands may be said as well to symbolize the rolling foothills of the Blue Ridge country; but, more important, these are the colors of our Blessed Mother.
The sinister impalement, on the right of the viewer, bears the personal arms of Archbishop Donnellan.
The oak tree from the coat of arms of the Donnellan family of Galway, the ancestors of the Archbishop, has been emblazoned on the personal arms, but the field has been changed from silver to gold that the Irish colors might prevail to pay homage to Saint Patrick, the title of the Cathedral of the Archdiocese of New York, where Archbishop Donnellan spent the early years of his priesthood.
The ermine spots at either side are derived from the coat of arms of Francis Cardinal Spellman, the late Cardinal-Archbishop of New York, by whom Archbishop Donnellan was ordained a priest and consecrated a bishop.
The chief (upper portion) is given to two spearheads at either side of a saltire. The spearheads recall that the archbishop's baptismal patron, Saint Thomas was martyred by these instruments. The saltire is the well-known symbol of Saint Andrew, the Apostle, whose name the Archbishop also bears. Saint Andrew, the brother of Saint Peter, is believed to have been martyred upon a cross in the shape of the letter X.
The motto, "Ministrare non Ministrari," is translated "To serve, not to be served." The full text of the scriptural verse from which the motto is derived reads: "... even as the Son of Man has not come to be served but to serve, and to give his life for the ransom for many." (Matthew 20:28). A motto expresses briefly an ideal, a plan of life and the spirit of the one who selects it.
The external ornaments are composed of the pontifical hat, with its tassels, disposed in four rows, all in green, and the archiepiscopal cross with double transverse tinctured in gold. These are the trappings of a prelate of the rank of archbishop.
Prior to 1870, the pontifical hat was worn in solemn conclaves held in conjunction with papal functions. The color of the pontifical hat and the number and color of the tassels were signs of the rank of a prelate, a custom which is still preserved in ecclesiastical heraldry.
Reference:

www.archatl.com
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