(1) Such bonds shall be issued pursuant to an order made by the board and by their terms shall be made payable on or before a date not to exceed ten years from and after the date of their issue, which latter date shall also be fixed by such order. They shall bear interest at the rate or rates as authorized by the board, which interest shall be payable semiannually at periods named; shall be of such denomination as shall be provided in the order directing the issue, but not less than one hundred dollars nor more than one thousand dollars; shall be numbered from one upward consecutively and each bond shall be signed by the president of the board and attested by its clerk: PROVIDED, HOWEVER, That any coupons may, in lieu of being so signed, have printed thereon facsimile signatures of said officers. Each bond shall in the body thereof refer to the improvement to pay for which the same is issued; shall provide that the principal sum therein named and the interest thereon shall be payable out of the fund created for the payment of the cost and expense of said improvement, and not otherwise; and shall not be issued in an amount which, together with the assessments already paid, will exceed the cost and expense of the said condemnation and improvement. Such bonds may be in any form, including bearer bonds or registered bonds as provided in RCW
39.46.030.