> the symbol for “woman,” a downward-pointing triangle with a notch at the bottom tip
It is curious. Today a pictogram of a woman is an upward-pointing triangle with some small details added, while a downward-pointing triangle with the same details is a man. Sumerians would use a wrong bathroom all the time. Or we would use a wrong sumerian bathroom if we time traveled there.
The symbol is a pubic triangle, so it is quite accurate in showing the distinction between a female and a male (the "notch" mentioned above is the cleft between the labia majora).
Similarly, the Egyptian symbol for male was just a relatively accurate drawing of the male genital organs.
The modern symbols shy from drawing the body parts that distinguish males from females, hence the drawing of the entire body with the addition of features that are sometimes, but not always, associated with gender.