I would say that about a third of cars in the Baltimore area and about half of cars in the Harrisburg, PA area have the yellow ribbons - some of them with other without the "god bless the USA" garbage on them, but all "supporting our mercen... err.. troops". I do not think that the number has significantly changed since 9/11, albeit the contents did.
Another observation - the number of pro-Bush bumper stickers also visibly increased AFTER the election - especially the ones on a white oval and a letter W with the imperial flag attached to it, thus equating the dear leader and the state, ein volk, ein reich, ein fuerher.
As to the types of cars displaying these fascist insignia - I do not think there is any regularity - both expensive models and junkers; cars, trucks, and SUVs have them - the only exceptions being ever more popular Hummers whose very form speaks for itself and there is no need for wimpy bumper stickers.
One more thing. When I listen to assorted "activistists," populists, and peaceniks like you, Carrol or Yoshie I think of the scene form the film _Cabaret_ when the protagonists Sally and Brian, together with the German aristocrat Max sit in a Bavarian restaurant, and Max explains how the Nazi movement can be controlled to achieve useful ends. A little boy starts singing a Nazi patriotic song, and soon all patrons stand up, sing, and extend their hands in the Nazi salute. The three go to Max's car and Brian asks Max "Do you still think you can control them?" Max shrugs as they drive away.
Monday morning naysayer or not - I will not be the one trying to sway ein Amerikanische Volk when ein Fueherer and ein Reich will call - I will be driving off like the Max character, or rather flying nach Osten.