I've seen the same thing. Kerry bumper stickers where you'd least likely find them. Evangelical church parking lots, Red states, red cities, pickup trucks with gun racks, cars with military institute insignias in the back window. Guys in the guard or reserve in uniform getting out of their cars at gas stations or dining establishments.
My theory was that there were a lot of students in the area, particularly at the School of Art and Design in Savannah, by definition one of those artsy-fartsy "liberal-arts" colleges that northerners send their kids down to because they don't want to get a real job.