Post made on message boards are publicly accessible. There is no such thing as a PRIVATE message board --- the entire purpose of having genealogy message boards it get responses to queries and to allow others to find data posted on the boards. If you don't want information publicly accessible don't post it on a message board.
I'm not sure what you mean by "brings up my message board SEARCH history" though...it would bring up your POST HISTORY but not what you have SEARCHED.
Joan