Rosettes and Revelations Pt.1: The Holy City - Koen Gheuens and Cary Rapaport

[Scarecrow]

Another way of understanding/interpreting the Tau letter as symbol:

As a Franciscan symbol, the TAU, resembling the Cross, is a sign of conversion. Because of his affection and devotion to the cross of Christ, St. Francis used this sign as his personal signature. For Francis, conversion implies a turning toward God and turning to one’s brothers and sisters.

Thus the TAU becomes for us a symbol of permanent conversion, the seal of the Kingdom of God, a call to the service of others. 

With this sign, Francis recovers a tradition that goes back to the prophet Ezekiel. The TAU for Francis and for us is a sign of hope and a reminder of the goodness and love of God. 
It challenges us to live as peacemakers and to promote the healing of all creation.