The tau is the sign used by St. Francis to wish peace to all he met. The tau cross is a common symbol of the Franciscan Order. It looks like a T. In the Old Testament, it is the last letter of the Hebrew alphabet. For Christians, the T came to represent the cross of Christ as being the fulfillment of the Old Testament and it also represented the means by which Christ reversed the disobedience of the old Adam and became our Savior as the "New Adam."
After St. Francis's conversion, he worked with a religious community whose main ministry was caring for lepers. These men wore the cross shaped like a T as a symbol of their trust in God to ward off the skin diseases. Eventually, St. Francis adopted the T as his own symbol. For him, it represented lifelong fidelity to the Passion of the Christ and a reminder to be an example of compassion for God's people.
Today, followers of St. Francis - laity or religious - wear the tau cross as an exterior sign, a seal of their own commitment to exemplify God's love and continue the ministry of Christ.
The symbol of Franciscan Alliance, is a tau cross with a giving hand and a receiving hand. The giving hand is generously prepared to minister Christ's healing to the weak, the suffering and the vulnerable. The receptive hand is ready to receive His healing power through our joyful, sensitive Franciscan ministry.