It's just a wave.
Four miles in. Breathing like a busted radiator. Another runner coming the other way. You hold up two fingers without really thinking about it. They do it back. Nobody says a word. You keep running. Later you won't remember what they looked like but you'll remember the wave.
We thought about that for way too long and then made a t-shirt about it, which honestly is kind of a weird thing to do. But here we are.