Near the end of the 1970s my parents bought a Saab. Soon they noticed cars flashing their lights at them. At first they thought they had their high-beams on. Then they thought the drivers were warning them about speed traps. Eventually they discovered that all the cars that were flashing them were other Saabs. Apparently this was all part of the informal society of Saab-owners (though I later learned that other foreign car drivers did the same thing when encountering a fellow driver).
Thus my parents joined a movement without even knowing it.