Well what purpose does the rule serve if it can't be enforced, if not signalling/norming?

Your premise is fallacious - at best, it is partially enforceable (like I said: whistle-blowers, intel), which gives it teeth (not necessarily much, but more than zero, which makes it useful to some non-zero extent).

Even at worst, it expresses intent, which has meaning to humans. We are humans. I can't force you to do anything, but I can ask you to. Don't disparage what it means to be humans talking to each other - it's one of the few things we have left on Earth.