Have you seen the movie Waiting?
THE BRAAAAAAIIIIINNNNN!!!
Paint “Your Message Here, $25.00” on the roof of my house.
You have a week. Cut down the trees and get creative.
I would spell out Google sucks on my roof with something and see if they actually post the image.
I’d contact MapQuest and/or Microsoft Live and charge them a ton of money to stick a huge advertisement on top of my house (maybe coordinate with the neighbors, too).
Big bull’s eye on roof. “Alien LZ” on roof. Cut something suggestive into the middle of a bigass tarp laid over the back forty. Heck, paint something rude on the bigass tarp, easier to fix later than painted roof. Yes, I do have a bigass tarp, why do you ask? 
I really like the mouse pointer idea!
A 20 foot long housefly. They’ll never figure out how it got into the negative.
Edit: Mouse Pointer wins!
Get as many people as I can to go up onto the roof of my building and lie down, naked.
Paint a huge “fool-the-eye” painting on a tarp and stretch it across the roof. The painting would depict a hellmouth, or another building, or a courtyard with a fountain, or something.
Google let people know for Australia Day last year, and people did various things. It’s amazing what you can accomplish with a few reams of paper and wire stakes, or even just a shovel and a beach.
If I knew they were going to fly over my neighborhood in Chicago, I’d paint a huge Kate Bush “KT Fem” symbol on the roof with black poster paint. It would be very cool for the handful of people who knew what it is and be baffling for the vast masses.
Bull’s eye on NEIGHBOR’S roof!
Get many gallons of Karo and red food dye, some prop weaponry (heck, real weaponry would be fine too!), and everybody in the neighborhood, and stage the aftermath of some hideous battle/massacre.