Okla. Stat. tit. 62, § 543

Each and every item of securities purchased as an investment under the first and foregoing section hereof shall be marked or stamped with a number, and so recorded as in form prescribed, which record shall not fail to disclose unmatured coupons attached to any negotiable coupon bond purchased; and the account of such treasurer with each such sinking fund shall distinguish between the cash and investments belonging thereto. Such record shall, as to any sale, make reference to the district court case authorizing the same and the effect of such order. Moreover, at the time investment is made, each and every item of such securities payable to bearer shall be marked or stamped: "This (item) is the property of the Sinking Fund of (naming the municipality) as an investment therein, and no assignment therein, and no assignment thereof shall have any force and effect unless it makes reference to the order of the district court authorizing the same.