What came first, the chicken or the egg? The button or the sign? These are some of life's biggest mysteries. You have to wonder if someone made the sign and then realized that the store only sold green buttons. "They'll get it." The thing is, people won't get it. We'll spend hours looking for a red button somewhere, afraid to press the green button. "No one said press the green button. What happens if I press that? Certain death?" That's exactly where my mind would go. I'd never end up entering the building at all.
I'm glad it isn't the other way around. If that was a random red button, no one would ever press it. Red buttons mean "don't press unless you want something bad to happen." At least green buttons are happy buttons. Good things happen with green buttons!