When I moved from the city to the country about fifteen years ago I was introduced to the index-finger-off-the-steering-wheel-wave that all male drivers around here give to each other. It's not an enthusiastic wave, just the driver's equivalent of a head nod or cursory "Hi". After years of mostly suburban and city driving it seemed odd at first to be casually greeted by other drivers, but it didn't take long to find myself responding to and, soon, initializing the wave. If someone doesn't signal back it's a sure sign that he isn't from around here. Oddly, the wave is seldom given to or received from female drivers and there's probably a truckload of stuff a sociologist could read into that, but I'm not gonna go there.