The seal is called "great" to distinguish this rendition from other renditions which contain only parts of the whole, such as the eagle, the vesica and shield, or shield with or without motto.

The shield which forms the heart of the seal is taken from the flag of Saint John, a dark blue field with a silver cross. The shield is surmounted by a heading of silver (white) which contains three distinct flowers growing from a single vine. The center flower is the Passion Flower, symbolic of Christ Jesus; the left flower is a stylized type of rose, representing the Virgin Mary, whose traditional flower is either rose or lily; the right flower is Saint John's Wort, borrowed from Saint John the Baptist to represent our Saint John, who has no traditional flower. Together, the three flowers depict the scene of the Crucifixion, with Christ on the Cross and Our Lady and Saint John beneath at either side. It at the same time a pictorial representation of the words of Jesus found in John's Gospel, "I am the vine, and you are the branches" John.15.5.

The blue shield has at its center the silver (white) cross of Saint John the Evangelist, dividing the shield into four quadrants. Superimposed on this silver cross is the red Cross of Saint George, patron saint of England, which is itself a representation of the Cross of Christ, and represents our heritage from and binding ties to the Church of England and the Anglican Communion.

In the upper left quadrant is the Eagle, symbol of Saint John, our parochial patron saint. This representation is identical to and meticulously copied from the rendering in the ceiling over the Altar in the present church.

In the upper right quadrant is an open Bible. The Bible is opened to the first chapter of Saint John's Gospel and reads: "In the beginning was the Word, and the Word was with God, and the Word was God. And the Word was made flesh and dwelt among us." John.1.1, 14. The seal has been devised so that, when sufficiently enlarged, this text is legible in three languages: the original Greek, the Church's traditional Latin, and in English. This represents Saint John's work as an Evangelist.

The lower left quadrant below the central Cross, where Our Lady is traditionally depicted in portrayals of the Crucifixion, contains the stylized monogram "AM". This is the cipher of the Blessed Virgin Mary, taken from the angelic greeting "Ave" found in the Luke 1.28 and from the first initial of her name Maria, both in the traditional Latin. It also has the further traditional meaning of "Auspice Maria", meaning "under Mary's patronage". The references to the Virgin Mary in the seal are a reminder that she was given by Jesus on the Cross to be Saint John's mother, and into his care. In the Gospels, she is both the model of the Church and a symbol of the Church. In the Communion of Saints she holds primacy of place and honor, and is an intercessor for the church. These references are also a strong reminder of the place of the Blessed Virgin in the history of our salvation and of the respect, devotion, and honor in which she is held by the people of Saint John's Church.

The lower right quadrant contains a Celtic harp which symbolizes our long parochial history of love for excellence in the music of the Church, particularly that of our English heritage. It represents the musical program which has been and is our parish's primary outreach mission.

Each quadrant is bounded by a gold border containing fleur-de-lis. The fleur-de-lis is taken from the walls in the sanctuary of the church where it is both a symbol of the Holy Trinity and our Trinitarian faith, and of the Virgin Mary, who is our model of faithfulness at the sacrifice of the Cross and present on our Altar.

Below the shield is the parish motto, adopted by the Vestry from John's Gospel John 8.32 and inscribed in the traditional Latin: "Veritas vos liberatbit", translated as "The truth shall set you free".

The shield is placed on an heraldic device called a "vesica", which identifies to all, again using the ancient Church's universal Latin language, that this is the seal of Saint John's Church, originally in the village of Huntingdon, now the city of Baltimore, in Maryland, and giving the date of its founding, 1843.

All of this is supported by an heraldic depiction of the eagle of Saint John, which offers to the world from one claw the Chalice and Host, the Bread of Life and Cup of Salvation John 6.51, 55-56, and from the other the cross-surmounted Orb, symbol of the reign of God in Christ over all Revelation 5.11-14.The artwork for this, the official seal of the parish, was executed as a gift to Saint John's Church by local Baltimore graphic design artist and friend of Saint John's, Gene Sartori, of Gene Sartori Designs.