This was the information that was posted when the sign sold at Sotherby's.
"The original name plates from the main iron gates to West Ham United`s Boleyn Ground installed circa 1904, the cut iron lettering mounted on two iron back-plates, painted silver on red oxide, the first reading WEST HAM UNITED, the second FOOTBALL CO. LTD., each 168 by 20cm., 66 by 8in. (2) Thames Ironworks FC was founded in 1895 by employees of this shipbuilding yard. Short of funds, the club was wound up in June 1900 and relaunched a month later as a professional club, West Ham United Football Co. Ltd. They moved from their original Memorial Recreation Ground, Canning Town, in 1904 to the Boleyn Ground, Upton Park."
Hopefully someone will recognise it, as it's the E,H and A are quite distinctive.