The Franciscan Tau Cross is also called the Cross of St. Francis or the Old Testament Cross. The Tau Cross is based on the Greek letter T. It is an uncomplicated cross and is considered a sign of life and salvation.
The Tau Cross was adopted by and worn by the many followers of St. Francis. In the Old Testament the mark of the Tau symbolized those having rejected a sinful live and in Revelations the sign of the Tau on the forehead signified someone belonging to Jesus Christ.
Pope Innocent III presented a sermon in 1215 referencing the Tau which was the inspiration for Saint Francis to use the Tau. It is widely believed that St. Francis was present during this sermon at which time he enthusiastically embraced the Tau cross as his symbol.