Parkerising is an American brand name for manganese(black finish) or zinc(shades of gray, depending on the metal it went on, finish.) based metal finishes. Other countries used black phosphate. Don't think there's any way to tell the difference by just looking though.
You can tell how "fresh" a finishing job is. Any sign of the finish being worn? Picture the finish on an M1 Rifle and how the finish can look worn off.
FN-49's were only made by FN in Belgium. However, there doesn't seem to be a good site with all the markings. Most places(a lot being just copies of the Wikipedia blurb) are saying very few non-Luxembourg .30-06 rifles made it Stateside. Then there's this that does list receiver markings by country.
http://weaponsman.com/?p=34897
Blake Steven's book 'The FN49 – the Rifle That Ran out of Time' would be the one to buy. He's kind of a thorough guy.
https://www.amazon.com/FN49-Rifle-Th.../dp/0889355266