In Archetypes of the Collective Unconscious, Carl Jung notes that “the companion to the chthonic mother is the ithyphallic Hermes or a lingam.” He adds “In India this symbol is of the highest spiritual significance” 
The lingam is an image of Shiva’s phallus, representing the spiritual energy and power of Shiva. The word lingam means sign or symbol or mark. The lingam, as symbol or mark, represents an energy that which is beyond words to describe. The lingam image is often shown along with an image of the yoni. In the image above, we see an ancient Lingam from the 1st Century BC. Wikipedia describes the image:
“The Linga is carved out of a hard dark brown indigenous stone. It is about 5 ft in height and one foot in thickness. The nut of the lingo is clearly differentiated from the shaft by a deep slanting groove cut about a foot from the top of the Linga. A beautiful two handed image of Shiva in sthanaka posture is carved in high relief. On the front portion of the Linga the God is standing on the shoulders of the apasmarapurusha or a dwarf. The Deity holds a ram in his right hand and a small vessel in his left hand. There is a battle axe (Parasu) resting on his left shoulder. His head is adorned with Jatas arranged in the Jatabhara fashion. He wears a number of rings in his ears and a unique girdle with a dangling central portion. The male image in front of the linga wears a dhoti fastened at his waist with a vastra-mekhala which covers whole linga, but is transparent”.
- The Archetypes and The Collective Unconscious (Collected Works of C.G. Jung Vol.9 Part 1)