A public officer shall not accept any such depository bond unless there is attached thereto a certificate, under oath, of some authorized officer or agent of the surety company to the effect that, at the time of executing the bond, no stockholder or director of the surety company furnishing the bond is a stockholder, member or director in any banking or trust company, insured credit union, insured savings and loan association or insured savings bank in which the public money is or is to be deposited knowingly.