"Thus the main motifs of the seal tablets emphasize two cultural phenomena. The first is that there was a rich mythopetic basis for the use of these motifs. The second is that the main motifs emphasize pan-settlement relationships, i.e. something held in common by the society at large, namely, the sodality to which the individual belonged. In contrast, we can assume that the Harappan writing identifies the indivudual who bears the seal tablet since the sign order is rarely duplicated. Here then is a clue to the meaning of the writing as it appears on seal tablets. With high probability it describes the individual who bears the tablet by name, title, occupation, social status, family, etc., in the conventional manner of time. In toto the large seal tablet motifs represent the sodality to which the bearer of the seal tablet belongs. The writing identifies the individual within the sodality." (William Fairservis, The Harappan Civilization and its Writing, E.J. Brill, 1992, p. 6).
Although William Fairservis later reading of Indus signs within this framework is not widely accepted, this is still an acceptable train of thought. Animals could well represent distinct ethnic, tribal, or what Fairservis calls "sodalities," a word which usually refers to task-oriented Christian religious groups and fraternities. An unusual word, but it may not be far off to see Indus groups as probably having a spiritual bond. Massimo Vidale suggests that the animal on the seal may represent a particular tribe with a specialty, like merchants. It is notable that most seals represent real animals, like the bull or water buffalo or elephant or tiger, but there is a healthy mixture of imaginary creature seals, and it is not impossible to think of the unicorn seal as taking the parts of other seals and representing them together in some sort of unified structure or ideology. This unifying force spread most widely across cities and towns around 2500-2300 BCE.