The bonds issued pursuant to this chapter must be in the form of negotiable coupon bonds, payable to bearer, but may be issued with the privilege to any holder of having them registered as to principal on the books of the county treasurer upon such conditions as the governing body may prescribe. Except when registered, all bonds issued pursuant to this chapter shall have all attributes of negotiable instruments under the law merchant and the Uniform Commercial Code. Provided, however, that any bonds issued under this chapter and purchased by the United States of America, or any agency or department thereof, may be in fully registered form as to both principal and interest and registered on the books of the county treasurer.