The Sacred Ganga Talao - Mauritius

A. L. Basham says that linga have been found in the Harappan remains, and provides these comments relating to the antiquity of the symbol:

Furthermore, there are instances in Hindu lore where a rock or pile of sand has been used by heroic personages as a Lingam or symbol of Shiva. For example, Arjuna fashioned a lingam of clay when worshipping Shiva. Thus, it is argued, too much should not be made of the usual shape of the Lingam. This view is also consonant with philosophies that hold that God may be conceptualized and worshipped in any convenient form; the form itself is irrelevant, the divine power that it represents is all that matters.

Hindu interpreters often use the underlying meaning of "sign" or "mark" for the Sanskrit word linga as the basis for their commentaries. For example:

Western commentators often use the concept of "male generative organ" as the basis for their interpretations. For example: - - *Monier-Williams provides one definition for lingam as: "The male organ... esp. that of Siva worshipped in the form of a stone or marble column...". - - *Gavin Flood's An Introduction to Hinduism refers to the worship of Shiva "in his form as the Śiva liṅga or 'icon' found in most Hindu temples. The linga represents a phallus..."

REFERENCE: http://en.wikipedia.org/wiki/Lingam