Collaboration with Obyvatelius
The Tau cross is a cross in the shape of a 'T' that acquired its name from the corresponding letter in Greek alphabet. This cross has a wide range of symbolical meanings. One of the most common is a sign of innocence.
In the second vision of Prophet Ezekiel God told to mark upon foreheads of the innocent with a special sign since he was going to discharge his anger upon enveloped in sin Jerusalem. "Then the Lord called to the man clothed in linen who had the writing kit at his side and said to him, "Go throughout the city of Jerusalem and put a mark on the foreheads of those who grieve and lament over all the detestable things that are done in it." (Ezek. 9.3-4). What in translation was called "mark" in original reads as "tau" - the last letter in Hebrew.
The TAU Cross was the sign which the Lord told the people of Jerusalem to mark upon their foreheads, as related by the Prophet Ezekiel. It was also placed as a symbol of liberation upon those charged with crimes but acquitted. MPHPhilosophical Research Society website, PRS.org
The Tau cross upon Manson's forehead in the Holy Wood artwork represents Manson's innocence. Holy Wood as an album and concept was Manson's retaliation against the media, the society and the America which had demonized and laid the blame upon him for such atrocities as the Columbine killings. The T-shaped cross which Manson wore on his forehead as a metal plate represents the Tau cross and thereby representing Manson's innocence of the unjust and grossly inaccurate blame laid upon him.
The Tau cross is also mentioned in the first song from the album, 'Godeatgod', in connection with the crucifixion of Christ:
Dear god can you climb of that tree
Meat in the shape of a 'T'
Which this was the shape in which Christ was crucified in; his arms outstretched and body lay vertical as a 'T'. In fact many of the hundreds of crucifixions which took place at the hands of the Romans, the cross actually bore more of a resemblance to a 'T' rather than the 't' which many crucifixes resemble.