Just did a little looking on Gunbroker and came up with several "F" prefixes, including "FC" "FE" "FR" and an "FG17352." As Jim Watson said, it's just part of Colt's alphanumeric numbering system used on Series 80 blued full size 1911s.
Absolutely nothing out of the ordinary here.
LOL!! Edit: I just went and dug my Series 80 out. SN FG204xx. I bought it in the 90s.
Last edited by gyvel; January 5, 2012 at 02:13 AM.