"...And in reality the Saint showed great veneration and affection for the Tau; while speaking he would often recommend it and write it himself at the foot of the letters he sent, as if his mission consisted, according to the words of the prophet, in marking the Tau on the foreheads of the men who wail and weep, honestly being converted to Christ.".
BONAVENTURA DA BAGNOREGIO, The Life of St Francis of Assisi
(Legenda maior), chap. IV. 1079
I got this Tau Cross from a trip to Furen Daxue in XinZhuang, Taipei a while back. Was just checking it's history and realized why it stays with me.