復帰ユーザーと新規ユーザーへの挨拶にはプライベートメッセージを含める場合があります

[Moin]

I think that is intentional

Post notices for first-time and returning users

No, this won’t be happening, the current behavior is very intentional. Your other option is CSS modifications, which you can easily make yourself as @pfaffman noted.