I don't think pointing out the flaws in a scheme is tantamount to 'rubbishing it'.
The problem is that, often, people don't really think about a scheme like this. It looks attractive at first glance, but it hasn't been thought through.
In the example above, a poster says It's not always easy to say "you weirdo, I'm outta here!" - we should be trying to change this - encourage women to feel that's absolutely fine to say you want to leave a situation in which you don't feel comfortable, when you are in a safe, public environment.
Inventing secret codes, that are neither truly secret nor universally understood, but fall in a middle ground which renders their usefulness minimal, is not the answer.
I'm disappointed that some people, rather than engaging in a reasoned discussion about schemes that might work, when others raise detailed and considered objections, are simply shutting down discussion by saying that anyone who doesn't think this scheme is marvellous isn't interested in 'helping women'.