Abbreviation (used in stylised form as a logo) of the Ferrovie dello Stato ("State Railways"), the Italian national railway system - an autonomous state owned corporation (Ente) founded in 1985. Operates just over 16000 km of lines and employs around 120 thousand people. A number of private companies also exist, running secondary lines.
Update: (2002-06-14) the FS is now trading as Trenitalia (see
http://www.trenitalia.com for useful stuff like timetables and on-line booking) but still uses the stylised FS logo.