This article has some pretty interesting information on the roots of the written symbols &, #, !, $, and =.

For instance the question mark:

Origin: When early scholars wrote in Latin, they would place the word questio – meaning “question” – at the end of a sentence to indicate a query. To conserve valuable space, writing it was soon shortened to qo, which caused another problem – readers might mistake it for the ending of a word. So they squashed the letters into a symbol: a lowercased q on top of an o. Over time the o shrank to a dot and the q to a squiggle, giving us our current question mark.