The crackle glaze is commonly used in todays ceramics/pottery and has been for years !! Only items that might have a serial number would be the limited edition pieces and they are marked as such !! Registration numbers were used in the UK !! Post a pic of an American piece with a known serial number because in 40 years of dealing with antique and vintage items I have never seen one !! !! It will say “serial number”, if it has one !! This has the K-10 and copyright symbol made in the mold so I know they did not make just one,, it was a factory piece !! In the USA any work of art,which would include this duck is automatically under copyright from the moment of its conception so there is really no reason to register it at all but many do for extra protection if its a unique design !!, I did not find this one as having been registered !!