I'll check at home and see, but it has been a policy for the last 45 years in all 20 congregations I have attended in the US and Europe. The KM was once known as the Bulletin so obviously it has not always been avoided.
http://oroborus21.com/jwnet/theocratese/=I.html#information_board
- information board
- A bulletin board. Most Kingdom Halls have some kind of bulletin board on which to hang schedules, letters from the {Society}, and other authorized printed matter. Although the common term for these is ``bulletin board'', the Society consistently uses the term ``information board''. Four people have written to inform me that this is because the origin of the word bulletin is connected with papal bulls, i.e., edicts from the pope. Various popes have certainly posted a lot of bull, so this assertion is believable. <<The Society says that we should not place personal announcements, messages, or thank-you cards on the information board.>> In United Kingdom, this board is called the ``notice board''.