random brain-spew

How did the question mark become the symbol for question? How did "s" become the symbol for the sound it represents? (Perhaps as a logogram evolved from a pictogram for a snake, then abstracted to represent the sound a snake makes?) This is what I get for reading a book on Sumerian Cuneiform.

Transliteration into English introduces myriad problems in pronunciation... X as Z (xenophobe, xerxes), X as the Chinese sound "sh" (xia, xiu), X as "ks"--ox, box. Can a symbol be a pure representation of either (a) meaning or (b) sound? Must it all be purely arbitrary and abstract?