Surely if the rifle was one of those made for and PAID for by the UK prior to Lend Lease it would not have been marked US Property?
Every Savage from 0C1 until the last rifle that came off of the line was marked "US PROPERTY". I have seen pictures of 0C1 and I have a small collection of Savage rifles from 0C37 thru 0C54632 and they all have it.