In contravention of such rules and regulations as the Commission shall prescribe for the protection of investors to hypothecate or arrange for the hypothecation of any securities carried for the account of any customer under circumstances (1) that will permit the commingling of his securities without his written consent with the securities of any other customer, (2) that will permit such securities to be commingled with the securities of any person other than a bona fide customer, or (3) that will permit such securities to be hypothecated, or subjected to any lien or claim of the pledgee, for a sum in excess of the aggregate indebtedness of such customers in respect of such securities.