Seeing faces or figures where there are actually none is a phenomenon called pareidolia.
Its is a function of the human brain that serves to fill in visual information using prior knowledge or experience. In the case of the moon, depending on the hemisphere from which you view it and the culture from which you come, you might see a pair of hands, a banyan tree, a rabbit, or in the case of Europe and the United States, a man's face. Man in the moon jewelry was a brief but notable trend in the late Victorian and early Edwardian periods. The focal point of these rare and collectible jewels is always a face carved from moonstone, saphiret, or glass, typically accented with a halo or crescent of seed pearls or diamonds. This man in the moon ring was converted from a brooch at some point in history. The finely carved moonstone face exudes a lovely adularescence within a surround of seed pearls.