Ref: 0009930-12-1: "Tau" Seal

This is an Italian seal that consists of a waxed, turned wooden handle and a bronze disc engraved with the "Tau" symbol, which is the Cross of Saint Anthony. This sign is reminiscent of the Cross; it is the sign of liberation.

Tau is the last letter of the Hebrew alphabet and has had symbolic value since the writings of the Old Testament.
The Tau is the sign placed on the foreheads of the poor of Israel, saving them from extermination.
Christians (especially the Franciscans) adopted the Tau because its shape reminded them of the cross on which Christ was sacrificed for the salvation of the world.
Saint Francis of Assisi often used this sign. He drew it on houses, walls, and trees. With this sign, he blessed people and signed his letters, a sign of blessing and peace.