Spanish speakers (when they're, erm, writing) use an upside-down question mark at the beginning of a sentence (in addition to the one at the end) to really ram home the fact that the sentence is indeed a question. What the hell is this symbol called in English?
If you click here, that will link you to the web-page of a 'Learn Spanish' site. According to them, the symbol is actually called - in Spanish, obviously! - "an upside-down question mark". So, you seem to have got the answer already.
My Spanish friend has emailed me this:
"It is called: "signo de interrogacion" and this is the same name for both of them � for the one that you write at the beginning and the one at the end. "
So even to the Spanish it's just 'a question mark'.