I can only think of 3 reasons to have a yard sign for a political candidate:
1. To raise awareness of that candidate's existence.
2. To encourage others to vote for that candidate.
3. To keep your grass from floating away.
Now, if you haven't heard of both McCain and Obama at this point, I don't think I want you voting in the first place. And last I looked, grass generally didn't just float away. So I guess it must be #2.
But does that really make sense? I can maybe see yard signs making a difference when it comes to city comptroller, but in this age of "You're either with us or against us, you dirty scum!" politics, is anyone going to swayed to vote for "the dark side" based on a yard sign?