The judge team have discussed this when we created the ref-pack. One of the reasons we ended up choosing to not put who has a yellow card in some public place was the fear it can be abused. If you know your opponent has a yellow card, you try to pick fights with him. Make him lose his cool. Be provocative, question everything he does, accuse him of cheating, and so on. You know that he is already on the judge's bad side, and that if he argues he risks being thrown out of the tournament.
We think the integrity of the tournament (avoiding helping people to abuse their opponent's yellow cards to their advantage) is more important that public shaming of people who cannot behave themselves.
Also, it's possible yellow cards will be handed to people who didn't do anything intentionally. There is a fine line between truly forgetting a rule and deliberately avoiding telling an opponent about it. Both actions can result in yellow card, but perhaps only the latter deserves to be publicly shamed.
All that said, if captain's don't agree with the judge team we will of course change this.