I have a policy of silent banning too. A lot of my members come from sites that love strife and contention so it is something that I have to deal with a lot. There are certain people that know that they aren't allowed there yet they will try to sneak in anyway.
If I were to make post about it or leave their posts in public view then they would be getting the attention they want so badly. If I don't say a single word and quietly ban them they get bored and go away. It's been almost a year since I opened Netwerkin and they still come back, and they still cause trouble at other sites and mention Netwerkin but I refuse to change my rules or my code of ethics to appease them.