If you read the comments on right-wing sites, you'll often encounter people who cite "signage" as evidence that the pollsters have deliberately under-counted Romney supporters. "Everywhere I go, I see yard signs for Mitt Romney. You never see Obama signs around here."
That's the kind of thing they say.
And they're right.
I can't recall the last time I saw an Obama/Biden yard sign in or around Baltimore. Romney signs are relatively common.
Yet everyone knows that Maryland is as blue as a suffocating Smurf.
Conclusion: The relative dearth of Democratic signage proves only that Dems don't dig signs. Personally, I would never use my car or home to advertise a candidate, just as I would never use my shirt to advertise a beer company or a sports organization.