The GRO Indexes are the name and surname as entered in column 2 of the death certificate, there should be nothing else entered in this column, such as decorations or qualifications, although titles will be e.g. Grosvenor Hugh Lupus (Duke Of Westminster) 74 Wimborne 5a 180, Dec 1899. The clerks making the indexes would copy exactly what is entered, and wouls assume that G.F.S. are his initials. As dawnsh suggests you could get a copy of the certificate, but this will just show what is in the index.
Stan