Do you know who that was?” Melissa asked as we drove across the causeway that links “downtown” Addison with what locals call the “West Side.” My wife asked the question because a man in a green pickup truck, headed the opposite way on the causeway, had waved in a friendly manner at us. I waved back.

“No idea, honey,” I replied. She nodded, shrugged, and fell silent — probably because she knew the subject needed no further explanation. We were, after all, in our former home town, a coastal Washington County village of some 1,100 souls who have, thankfully, not changed much since we moved away some twenty-five years ago.

The inclination to wave to the driver of an oncoming vehicle still lives in many small distant towns, although it remains a bit of a mystery to most urbanely oriented Mainers. And in truth, the habit extends beyond just the back roads and hinterlands. But I suspect the reasons for waving differs somewhat from place to place.

In places like Addison, I learned long ago that waving to the driver of a seemingly familiar oncoming vehicle goes beyond mere friendliness. It is a sign of camaraderie and mutual alliance, a sort of admission that “we’re in this together, and we need to stick together.”

Like many other rural Maine towns, Addison was, and still is, a tough place to make a living. When my wife and I lived there, we learned daily the importance of good neighbors and taking care of each other. When it’s twenty-two below and your car won’t start, it’s a fellow Addisonite who will come to your aid, not some automobile insurance outfit. In such a place, a wave acknowledges to each other our mutual risks and benevolence.

There are, of course, limits on this handheld sense of amity. Had I been driving a brand new, tricked-out Lexus or Mercedes, it is unlikely the Addisonite in the green pickup would have acknowledged us. Such vehicles are clearly not local. As it was, our aging Subaru, with its similarly tarnished driver, meshed with Green Pickup’s expectations of a local vehicle and driver. My faded old flannel shirt probably helped, too.

Even so, another driver might have missed Green Pickup’s wave. Most of the time, the wave from an oncoming driver is a subtle signal. It’s largely a one-handed affair — a few fingers off the steering wheel, sometimes moved in a single motion to one side or another, sometimes just raised briefly and motionless in salutation. It is easy to miss.

But if someone really knows you and hasn’t seen you (or your car) around for some time, you might get a hand-off-the-wheel wave. This is a vigorous openhanded wave, with quick side-to-side movements, not at all like your Queen-of-England’s languid wrist-swivel wave. After the Green Pickup encounter, we saw a couple of those energetic waves, too.

I should mention there is also a male-female component to this roadway waving, in my opinion. Generally, women only wave if they actually do know who it is in the oncoming vehicle. And then, it’s only in response to the wave of the other driver. If I had to hazard a guess (and I don’t, but I’m foolish enough to do so), I would suppose women prefer to avoid ambiguous signals, particularly to men in only slightly familiar vehicles. It’s a self-preservation thing, I expect.

Waving is even more pronounced and common when one is in a boat on unfrequented waters of the Maine coast. It is also of a different quality entirely and, again, increases in intensity the farther you get from large population centers.

“Why are they waving to us?” my eight-year-old niece asked a few summers ago. She was visiting my wife and me in Arrowsic for the first time from her home in the Philadelphia suburbs. We were in our little, locally built runabout, far up the Kennebec River near Richmond. The few boats that passed us early that picture-perfect July day all contained male and female passengers who waved vigorously at us.

“I guess because they’re happy to see us,” I replied, sweeping my hand at the mostly-empty shores of Swan Island to the west and Dresden’s Eastern River to the east.

Alissa thought about this only for a moment, smiled in silent agreement, and then began waving energetically at every boat we met for the rest of the day. All but one responded in kind. “Hey, they didn’t wave,” Alissa said in a disappointed, plaintive voice. “What’s wrong with them?”

“Maybe they’re just not very happy,” I suggested.

“Too bad for them,” she said, waving at the next boat, whose passengers waved back. Alissa smiled as they responded and all seemed right in her world again. A Maine wave does work wonders.