I think its a Tau Cross
Most commonly today, the Cross of Tau is known as the symbol of St. Francis. It is “widely believed” that Francis attended the Fourth Lateran Council in 1215AD, where Pope Innocent III described the Cross of Tau as having “exactly the same form as the Cross on which our Lord was crucified on Calvary, and only those will be marked with this sign and will obtain mercy who have mortified their flesh and conformed their life to that of the Crucified Savior.” Shortly after that, Francis became a bit obsessed with the TAU, using only this symbol as a signature when asked to sign his name to something and drawing it on the doors and walls of places where he stayed. He, like many, thought of it as a sort of protection and aid in health and general well-being. St. Francis’s followers, inspired by the saint’s use of the symbol, quickly adopted it and turned it into the overreaching symbol of everything St. Francis stood for in his life and teachings.
OK, but what IS it?
“TAU” is based on the Greek letter “T”, pronounced in Hebrew the same way but written as an “X”, the last letter of the Hebrew alphabet. Its been used in religious ceremonies for thousands of years, possibly starting with the Ancient Egyptians who mounted it to an oval (“Ru”) and called it an “Ankh”. It’s appeared in Greek, Roman and Norse mythology, and was sited by name in the Book of Ezekiel: “Mark Thau upon the foreheads of the men that sigh”. (Ezekiel 9:4 DRA) For that reason, it is sometimes called the “Old Testament Cross”.
Some theologians and historians believe that Jesus was crucified on a Tau Cross, not the four-pointed cross that represents the Christian church today. This is one thing that Pope Innocent III spoke of, and perhaps one reason Francis took it as his symbol.
St. Francis wasn’t the first to embrace the symbolism of the Tau Cross, though. In the third century AD St. Anthony the Abbot of Egypt, thought of as being the father of the monastic tradition, walked with a crutch in the shape of the Tau Cross. When he would enter a cave to meditate or visit a fellow holy man, he would leave the Tau Cross outside as a symbol of communication with God to any who would pass by.
The Antonines, the monastic order of St. Anthony, was supposedly started by a French nobleman in 1095AD after the saint appeared to him in a vision, instructing him to plant a Tau Cross in the ground to help cure his son of disease. After that, Tau Crosses were worn as amulets throughout much of the Middle Ages to protect against sickness.
Across cultures, across millennia, the Cross of Tau has been a symbol of life, immortality, resurrection and general well-being.
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