The auto broadcast is not necessarily advertising, but rather used to help new players, or to keep others up to date if there is important news coming up. I do not see why you would want to avoid this, it is not that aggravating, and only comes up every once in a while. I am pretty sure that because it is automatic, it will show up to everybody no matter what, however, I can check if it would be possible to remove them with a command. Only thing is, I think the command would remove all of the broadcasting, as it does not seem possible to have only half of them show up on your screen, and all of them show up on somebody else's.