I usually only notice when my stride begins to alter unnaturally: steps shortened, or lengthened, a little hop to make it fit. My toe hugs the edge, and then, a few steps later, my heel just barely squeaks over the line. I know what's going on here.
It's fine. Nothing happens if you step on a crack. I know that. So step on the crack. Step on it. STEP.
I pull my feet forcefully back into line and place my foot deliberately on the seam. I step on another. Until finally I'm walking normally again, not paying attention.
See? No broken backs.
When I was a kid I would jump on the cracks viciously anytime I was mad at my mom. I'd get a running start on a good crack and pounce, pounding my feet into the pavement. I'd hold both feet flat, parallel to the sidewalk, and slap them down, again again again.
It was a time when I hadn't yet learned that it's no good to fight fire with fire, that's it's much better to use cool water.