The red shield with three gold crowns represents the three kings buried in Tynemouth Castle and may be seen on the organ in the church. The story below is taken from Wikipedia with links in yellow.

Oswin, king of Deira was murdered by the soldiers of King Oswiu of Bernicia, and subsequently his body was brought to Tynemouth for burial. He became St. Oswin and his burial place became a shrine visited by pilgrims. He was the first of the three kings buried at Tynemouth.

In 792 Osred II, who had been king of Northumbria from 789 to 790 and then deposed, was murdered. He also was buried at Tynemouth Priory. Osred was the second of the three kings buried at Tynemouth.

The third king to be buried at Tynemouth was Malcolm III, king of Scotland, who was killed at the Battle of Alnwick in 1093. (This is the same Malcolm who appears in Shakespeare's Macbeth.) The king's body was sent north for reburial, in the reign of his son Alexander I, at Dunfermline Abbey, or possibly Iona.