I also live in a fairly liberal Philly suburb — in 2008 there were at least 5 Obama signs visible from my front curb. This year = NONE — there are no Romney signs, either, but that’s not unusual, as there may have been only 2 or 3 for McCain in the entire neighborhood. I think many conservatives here feel “threatened” (for lack of a better word) and just vote quietly and don’t discuss.
Where I live, I get hassled by Dems. I had a McCain bumper sticker and had a mob of African Americans surround me yelling insults, about a week before the last election. At the polls they get aggressive, make you promise to vote Dem. If you don't, you just know you may have car problems when you come back out, or get a baseball bat in the face. So I agree with them, tell them I will vote Obama.
I no longer put bumper stickers on the car. It's too dangerous.