Haw. Rev. Stat. § 90
That Hawaiian postage stamps, postal cards, and stamped envelopes at the post-offices of the Hawaiian Islands when this Act takes effect, shall not be sold, but, together with those that shall thereafter be received at such offices as herein provided, shall be canceled under the direction of the Postmaster-General of the United States; those previously sold and uncanceled shall, if presented at such offices within six months after this Act takes effect, be received at their face value in exchange for postage stamps, postal cards, and stamped envelopes of the United States of the same aggregate face value and, so far as may be, of such denominations as desired.
Hawaiian currency: See Act of Jan. 14, 1903, c 186, 32 Stat 771, 48 U.S.C.A. 513-517.
HRS § 90