The M1917 Enfield, the "American Enfield" (frequently misidentified or mislabeled as the "P17", "P1917", or "Pattern 1917"), formally named "United States Rifle, cal .30, Model of 1917" was an American modification and production of the British .303 caliber P14 rifle developed and manufactured during the period 1917-1918.
heres a web page with good history and info for you
as for three marks the "s" with the radiating lines is a makers mark ( under licence ) for eddystone (sp?)
the X with the P under it , is this it or a variation of this it ??
( without pic's this is awful hard eh )