That's 100% true in the abstract sense that meaning is conventional/contextual, but that doesn't mean all conventions are equally intuitive. The rule "Top mean

That's 100% true in the abstract sense that meaning is conventional/contextual, but that doesn't mean all conventions are equally intuitive. The rule "Top means stop, bottom means go" is specific to traffic light context. The meaning of the word "Stop" is much broader as it is used in more contexts. (Of course, some people can't read, which creates a bunch of other problems). Maybe a better way to illustrate my point: I think traffic light are better at highlighting the problem of how to properly do semantic redundancy than at actually solving that problem (and that this is in part because colors are not accessible). FYI, I'm not some kind of accessibility zealot, I think it's just an interesting design problem.