When I was baptised I understood the 'sign' as
'the act of God's Son in receiving authority from his Sovereign Father to rule in an everlasting kingdom. This event brought the establishment or "birth of his kingly rule.
...This visible sign follows after and results from the invisible "sign of the Son of man," since it is composed of the many events and conditions that the Bible fore told would follow and result from the establishment of Christ's Kingdom rule it is , therefore a composite sign...'(WT 1966 Jan 15 pg 38)
The sign being in verse 30 of Matthew 24.
In the book "Things In Which It Is Impossible For God To Lie" (WT 1965) page 339 in the footnote it mentions that the Greek word for 'sign' is the Greek Septuagint of the Hebrew scriptures is given the meaning of 'standard, signal, ensign.' (Isaiah 11:12) and 'The Bible translation by Dr. Ferrar Fenton uses the word "signal" in Matthew 24:3,30.'
The book Man's Salvation Out of World Distress At Hand! (WT 1975) subheading "A Signal For The Peoples" page 197 after quoting Isaiah 11:10 it says, It is "in that day," since the Gentile times ended in 1914 C.E that this must occur.
page 198
However, the prophecy applies more particularly "in that day." We have been in that day since the birth of God's Messianic kingdom in the heavens in 1914 C.E. Then the glorified Jesus Christ, "the root of Jesse," stood up in Kingdom authority to deal with all the nations of the earth. (Matthew 25;31,32)
Fisherman your questions
What is the "sign" of "Christ's Invisible Presence?"
Have you seen "the sign" that the WTS refers to as the sign that people refuse to see and will be forced to see when the "son of man is revealed?"
I agreed at my baptism with the Watchtower in 1966 when it said
'There is one sign today that is of the highest importance to every person on earth. For us to see it, to understand it correctly and to act in accord with it promptly will spell the difference between life and death for each of us.'
and i was one who was part of 'over a million persons in all parts of the globe today acknowledge that they have been enabled to "see" "the sign of the Son of Man" and recognize its meaning' (WT 1966)
However in the February 15th 1994 Watchtower page 20 it says,
'But Matthew 24:30 points forward to a further "sign" appearing in the future, that of "the Son of Man," and all nations will be compelled to take note.
In answer to your question I am unsure due to how i understand the changed view and can no longer support them in preaching.