At the time of his admission to the hospital and once during the first six months of hospitalization and annually thereafter a voluntary patient shall be informed in writing of his right to release. The patient’s spouse, parent, legal guardian or other interested person shall also be so informed and shall sign a statement to that effect which shall become a part of the patient’s record. The patient shall also acknowledge deliverance of the notice in writing or an affidavit that he was so informed shall be attached to his record. Where no spouse, parent, legal guardian or other interested person is known to exist, documentation in the patient’s record of this finding will be deemed to be in compliance with the notification requirements.