How to select the main element from two characters?

Question

User interface

Two characters are given. One is assigned the attribute "main". How would you highlight it?
Specifically, these are two water pumps - a circle, inside which is a triangle of green (work) or black (stop) color.

Answer 1

The question is eloquently worded. "How would you distinguish"? Well, for example: "words", "luminous tape", "special font" or "deep embossing" - will it work?
But seriously, a normally formulated question should contain at least a hint of what means and, most importantly, why - you want to do this. Is that a sign that hangs on the door? Or is it an element of a poster on the classroom wall with an explanation for vocational school students? "How to isolate" strongly depends on this. In addition, it is not clear why - if "do not stick your hands out" then you need to highlight it not in green, but in red, for example.
And if the display is on a computer screen, then maybe it is necessary not to black, but to indicate a non-working mechanism in gray?
Well and still - in your example what attribute "main"? A circle, actually denoting a pump or a triangle (by the way - why a triangle)? Why isn't just colorful circles enough? Or do you not have a circle, but still a "circle"?