Shift + Option + ?

This question prompted by a suggestion from Merlin Mann’s Wisdom Project:

If you’re only tentatively committed to a calendar item—especially if the time of the event has not been mutually confirmed—title the event using Spanish-language questions marks. A future event like “¿Pick apples with Aunt Sue?” successfully blocks out the time while also affording a quickly scannable reminder about events that still need to either be formalized or deleted.

I like this idea, but to use it I need a fast way to type an upside-down question mark. I used the Keyboard Viewer to experiment with modifier keys until I found this combination.

This is likely specific to my British English keyboard layout; I imagine Spanish keyboards have a different layout that make this more convenient.