Symbolism, Imagery, Allegory
Drawn like a cross with a loop at the top, the ankh is an ancient Egyptian symbol for life. Even Sadie, with little knowledge of Egyptian stuff at the novel's start, knows an ankh when she sees one. Sadie has kept a picture of her mother holding her as a baby "because of the symbol on Mum's T-shirt: one of those life symbols—an ankh. My dead mother wearing the symbol for life. Nothing could've been sadder" (3.30-31).
The ankh also appears in the name of the Per Ankh, the House of Life, a.k.a. the Secret Egyptian Magicians' Club. The hieroglyph shows a rectangle surrounding an ankh, basically depicting a house… of life. Because of Sadie's mysterious ability to suddenly read hieroglyphs, she takes one glance at the symbol as it appears in the Brooklyn mansion and figures it out:
"It's a house," she insisted. "And the bottom picture is the ankh, the symbol for life. Per Ankh—the House of Life."
"Very good, Sadie." Amos looked impressed. (5.59-60)
It makes sense for the symbol of life to be so persistent in this book, since the episode that set events into motion for the Kane kids was when their father tried to release Osiris—a god of life and death. It all comes full circle, yo.