The shape is loosely based on a jewel that the Shriners (a fraternal organization) use as a decorative element in their ritual garments. Although I am not a member myself, I collect antique jewels from all kinds of brotherhoods (and sisterhoods). To create a feeling of reverence, elements from diverse cultures were often mish-mashed together - for example, the crescent was probably appropriated from Islamic art. The keystone bail, engraved with a brick-wall pattern, references the Masons, who were builders. And please note that I am in NO WAY an expert on fraternal jewelry - I just like it and am inspired by it. This is a very, VERY simplified explanation of the elaborate meanings behind fraternal symbols. If you want to truly dive into the mystical symbolism of the scimitar and crescent, I suggest you start here.