A common acknowledgement when driving on one lane (with lots of pullouts) Forest Service gravel roads is to raise a finger from the wheel as a salute, but when driving out there it has a meaning - if one finger is lifted that means there is one more truck behind the one you're passing, and if two fingers are raised, there will be two, so if you're at a wide spot just pull over and let them pass. Those roads aren't built for typical neighborhood traffic, they have gravel trucks, logging trucks, and lots of pickups of various sorts. Forest Service fire fighting trucks loaded with water were one of the few trucks the gravel and log trucks would slow and pull over for.

I usually give a wave to neighbors driving past if I'm working in the yard and always offer a wave when out walking the dogs (eye contact helps to make sure they see us there on the street).