The city director of finance and the city treasurer, or either of them, is authorized to negotiate the terms and conditions of contracts for the sale of short-term obligations as authorized by RCW Chapter 39.50 up to the maximum of the then-estimated costs and expense of each local improvement district. Such contracts shall be executed in the name of the city by the mayor, and attested by the city clerk, after approval as to form and legality by the city attorney. Unless otherwise provided by ordinance relating to a specific local improvement district, the obligations thus authorized may bear a fixed rate or rates or a variable rate or rates of interest which may be based on a bank prime or the most recent prime rate of interest published in the Wall Street Journal, but in any event shall not exceed a net effective interest rate of twelve percent per annum. Such short-term obligations shall be dated as of the date of their issuance and shall not be outstanding, together with any other short-term obligations issued to redeem the same, for longer than the time permitted by RCW Chapter 39.50. Such short-term obligations shall be registered in accordance with Chapter 3.18, as now in effect or hereafter amended, if so required in order to exempt the interest thereon from federal income taxation, and the city treasurer may designate which short-term obligations are those described in Section 3.18.030(D) as “obligations not usually subject to trading.” (Ord. 1405-87 § 1, 1987.)