Moksha is a concept, just like life after death & re-birth. We have various incidents where some child remembers things about previous life. Looking at these incidents we conclude that there may be life after death. Can anyone provide similar proofs that any human being has attained Moksha? Any sign, any scriptures providing signs of proof that a human being has attained Moksha after his death?
There are no signs or proofs that a person has attained moksha after death to the ordinary person. Similarly, there is no sign or proof that a living man has attained moksha. In his Pancadasi, Sri Vidyaranya Swami says (VI. 287-288):
Enlightened men may differ in their behavior because of the nature of their fructifying Karma. This should not make the learned think otherwise about the truth of knowledge resulting in liberation.
Let the enlightened people behave in any way according to their fructifying Karma, but their knowledge is the same and their liberation is the same.
and in his commentary on the first verse, verse 287, Swami Swahananda says:
There is no uniform rule about how a knower will behave. A well-known verse says: 'Krishna lived a life of enjoyment, Suka renounced even before Vedic initiation, vast empires were ruled by Rama and Janaka and Vasistha was a great ritualist, but all of them had the same illumination.'
And in the Introduction to Swami Swahananda's translation of the Pancadasi, T.M.P. Mahadevan says:
The final court of appeal is experience,--the plenary experience, which is the fruit of inquiry. In fact, the texts of scripture are but indicators of that experience. Thus, in Vedanta, the nature of Truth is sought to be expounded on the triple basis of scripture [hearing], reasoning [reflecting], and experience [meditating] (srutyuktyanubhutibhyah, V, 56, & XI, 89).
I am posting below Swami Vivekananda’s initial experiences reported by Swami Nikhilananda’s introductory essay in his book ‘The Gospel of Sri Ramakrishna’.
During his second visit, about a month later, suddenly, at the touch of the Master, Narendra felt overwhelmed and saw the walls of the room and everything around him whirling and vanishing. "What are you doing to me?" he cried in terror. "I have father and mother at home." He saw his own ego and the whole universe almost swallowed in a nameless void. With a laugh the Master easily restored him. Narendra thought he might have been hypnotized, but he could not understand how a monomaniac could cast a spell over the mind of a strong person like himself. But during his third visit Narendra fared no better. This time, at the Master's touch, he lost consciousness entirely. .... A few more meetings completely removed from Narendra's mind the last traces of the notion that Sri Ramakrishna might be a monomaniac or wily hypnotist. ... ..Narendra, because of his Brahmo upbringing, considered it wholly blasphemous to look on man as one with his Creator. One day at the temple garden he laughingly said to a friend: "How silly! This jug is God! This cup is God! Whatever we see is God! And we too are God! Nothing could be more absurd." Sri Ramakrishna came out of his room and gently touched him. Spellbound, he immediately perceived that everything in the world was indeed God. A new universe opened around him. Returning home in a dazed state, he found there too that the food, the plate, the eater himself, the people around him, were all God. When he walked in the street, he saw that the cabs, the horses, the streams of people, the buildings, were all Brahman. ..... It took him a number of days to recover his normal self. He had a foretaste of the great experiences yet to come and realized that the words of the Vedanta were true.
The Gospel of Sri Ramakrishna translated by Swami Nikhilananda