According to German April issue of Our Kingdom Ministry, the Watchtower logo must be removed from all Kingdom Halls:
It sais that the Watchtower logo - a stylised watchtower or a watchtower with a Bible - is used by the Watchtower Society. Thus, it should not be used by congregations or private persons, neither on Kingdom halls, stationary or anything else. People might think it would be an official building or letter of the Watchtower Society though it is not.
The logo must be removed from all kingdom halls, except where that is difficult; in these cases, it must be removed when the building is renovated next time.