To legally hunt waterfowl in WA, you need a small game license, a migratory bird validation (the old state duck stamp) and a Federal Duck Stamp with your name signed across its face. I attach mine to the back of my hunting license.
Many license dealers carry the Federal Duck Stamps as do most Post Offices. However, after dealing with a license vendor that no longer carries them and an ignorant Postal Clerk

, I decided I'd had enough B.S. for a morning and simply ordered mine on line from the U.S. Postal Service website:
www.usps.comOn the site, merely search duck stamps and you will find them. Shipping is all of one dollar; no matter the quantity.