In hopes of finding out more about the petroglyph, I googled "petroglyphs in Greenfield area" and stumbled upon a Greenfield Recorder newspaper article entitled "Native Insight: There Must Be Native American Petroglyphs Left to Find in Our Valley" written by writer/historian Gary Sanderson of Greenfield, MA. Gary is a 25-year, senior-active member of the outdoor-writers association of America. I contacted Gary and he did the heavy lifting required in solving the mystery of the strange image looking out from the standing stone. He recently posted the results of his research on his blog, Tavernfare.com. Seems it was serendipity that I should've contacted Gary.