I wrote:

I'm pretty sure it is important that it be noticed by the punished agent that the punishment is ...

On further thought, that was silly of me. It is not just the person being punished who needs to know that (and why) the punishment is happening. Everyone needs to know. Everyone in the coalition. Everyone who is considering joining the coalition. And, if not everyone, then as many of them as possible. In theory, the punishee is not in any special position here with respect to "need to know". (In practice, though, he probably does have a greater need to know that he is being punished because he may not have known that his 'crime' was a punishable offense. Also, if he doesn't realize that he is being punished, he might feel justified in retaliating.)