According to what I know, The ת Tav represents a mark, stamp, or seal. For example, in ancient times, would someone wrote a letter they would seal it with wax; an official document would receive an impression, a stamp, a seal in that wax; this is what the letter Tav represents.

The Tav means “cross,” and is the final letter of the Hebrew alphabet. It is numbered 300 in the Greek and 400 in the Hebrew numerical alphabet. The tau corresponds astrologically with the planet Saturn and the concept of finality. The mark was associated with the absolution of sin and may have been the original “mark of Cain” of the Old Testament. In the Hebrew kabbala, the Tav represents the completion of creation and is an emblem of infinity. In the visions of Ezekiel, it is the sign etched on the foreheads of priests and initiates. The Greek Tau is associated with the letter Theta, an emblem of death originally symbolized by a cross in a circle or a skull. :)

Thanks for sharing your wisdom @hebrew :)