I am quite sure that it is a copy. I have a Redhead decoy from their mold and on the bottom of the decoy it has Decoys Unlimited - Clinton, IA. The decoy is a sample from them and I bought it in 1972. John
i would also say copy. i have many DU molds and they are all marked.
i also have some copies my grandfather made in his foundry ant they work great .
yours should too.