As a sign, ankh is unambiguous: life, breath, used across every period of Egyptian writing, temple relief, and funerary art, held to the noses of kings and mummies as the breath of eternal life. What the shape depicts is unsettled: Gardiner argued a sandal strap, the word for sandal sharing the root nkh; Budge and Westendorf argued the tyet, the knot or girdle of Isis; others see an umbilical cord looped and tied to a stick, life flowing from mother to child as the ankh flows from god to human. Coptic Christians adopted it as the crux ansata, the handled cross.
Popular tradition calls it the key of life or key of the Nile, unlocking death's gates, a reading modern esoteric orders, Rosicrucians among them, enthusiastically adopted. The key idea is nowhere in the Egyptian sources, but it is functionally what the painted ankh does in tomb scenes: it is the instrument by which gods hand life over. Egypt made vessels, mirrors, sistra, and bouquets in its shape. It was less a symbol than standard equipment.
The claim: the ankh's endurance, four thousand years, from temple wall to Coptic altar to jewelry counter, comes from being the one symbol that promises the only product nobody can verify or refund, life after death, making it the oldest logo in the hope business. Verdict: cynical but structurally accurate, the ankh's brand has outlived every civilization that minted it. Yet the shape debate is the tell: we wear the symbol without knowing what it is a picture of. That is not a flaw in the product. That is the product.
If the shape is a mystery, why did every god in Egypt carry one?