Here's the flag that everyone is looking for. This embroidered pin flag from the 2018 US Open at Shinnecock is autographed by the Champion Brooks Koepka. Koepka is a difficult signer, especially on flags from his Major Championship victories. Any Brooks Koepka signed flag would be coveted by collectors, but this example is extraordinary and contains a huge, full-signature Koepka autograph.
Certificate of Authenticity from Green Jacket Auctions (GJA)