I was reading Eats, Shoots & Leaves and came across a bit which passes on the suggestion that rhetorical questions could be indicated by the upside down question mark the Spanish use at the start of questions. Apparently this was actually the practice at one time back in teh 17th century.

For example:

Do bears shit in the woods¿

(You get that by holding down Alt and typing 168 on the numeric pad on your keyboard.)