[madeofpalk]

You don't just press the button and see what happens?

[whywhywouldyou]

That's the point. Adding the LED does very little to help the user understand the state. In the end, you'll just push the button anyway to make sure.

[oneeyedpigeon]

In the UK, where this kind of behaviour is the default, we just learn it from a young age, possibly at school.

[function_seven]

If the indicator light is on, the OP presses the button, and that same indicator light remains illuminated: What did we learn?

It could still be a, “hey, press the button” light. Or it could be a “button already pressed” light

[mayneack]

That's true if you only ever press one light. You can still learn the pattern in a given area with experimentation (assuming most lights work the same). I know, for example, that lights in LA indicate that it's already pressed, but would have to experiment in a new city.