Lord Siva as Dakshinamurthy always indicates to us the direction. In a temple, the linga may face any direction, but Dakshinamurthy always faces the south. Significantly, Dakshinamurthy has cin mudra, the same one Lord Siva used to reveal the Supreme Truth to the sons of Brahma, D. Gnanansundaram said in a discourse.
The Lord was doing penance and was observing silence. The sons of Brahma came to Him and said they had studied the Vedas, but had not gained the knowledge they sought. They had the feeling of being caught in an ocean on a stormy night. That is the feeling one could get upon reading the Vedas, because the Vedas are difficult to understand. That is why the Agamas came later, to elucidate what the Vedas talk about. There are both Saivite and Vaishnavite agamas.
The Vedas were not written by human beings, so they are referred to as being apaurusheyam. Swami Vivekananda used to say that the word ‘discover’ was often wrongly used. For example, how can we say Newton discovered gravity? It is not as if there was no gravity before him. He was the one who understood how gravity worked and explained it to the rest of the world. Thus, he revealed his knowledge to others. In the same way, the Vedas are a revelation, and are the embodiment of knowledge, but they are unfathomable. So it was that the sons of Brahma could not get gnana by studying the Vedas.
Lord Siva revealed the Supreme Truth to them through cin mudra. The Supreme One is described as being with us, but different from us and yet always with us. The Lord is with us, but He does not experience what we experience in this world, and so He is different from us. He is always with us, never leaving us. The thumb is akin to the Lord. It is a part of our five fingers, yet it stands apart from the other fingers. But we can do nothing without the thumb. The index finger points to human beings, full of frailties. The middle finger indicates self, which brings with it pride and desires. The ring finger indicates karma. The little finger indicates illusion (maya). If we can distance ourselves from pride, karma and illusion, then we can reach God. Thus the Truth was revealed by Lord Siva symbolically.