Good for Hamilton! Big part of my childhood.
To the gender point, girls were always welcome in our games, but only rarely participated.
The thread title is spot on. That's exactly what we yelled every time a car came. Each time we dutifully moved the nets out the way to let the car through. It was a relatively quiet neighborhood street, so we weren't interrupted all that often.
Years later I learned that my Grandmother rather disapproved of the practice. To my Mom's eternal credit, her response was "Lighten up, that's how things are done here." But my Grandmother remained convinced that the day would come when the proper authorities would put a stop to the criminal activity.
Well, there finally came a day came when the "Car!" was a police car. My Grandmother, watching out the front window, is reported to have said something like "It's a shame that the boys will be arrested, but justice must be served."
So what actually happened? The Officer gave a cheerful wave, and turned the corner to avoid disturbing the game. We cheerfully waved back, and resumed play.
Grandma was aghast. Her next reported comment was that our evil city had descended into lawlessness, if not utter depravity. And then something about the moral superiority of her small town.
Pretty juicy stuff. But my parents withheld that story from us for years. Until we were old enough to see the levity and not have hard feelings, I suppose.
I should make it clear that I loved my Grandmother dearly. But she was wrong about street hockey.