Hi Gerry,
1. The broad arrow is the Britishicon Government inspection and acceptance mark
2. The crown over GR over flags over P is the British military proof mark
3. The crown over N is another British inspection mark
4. I think the .303 Nitro Proof is a British civilian re-proof mark, indicating that the rifle went abroad at some time and was reproofed when returned to the UK.
5. The '17 is the date of the barrel. This is a British mark (not American) so would indicate the year of British proof but most likely the year of manufacture as well. P14's were only made in 1916-1917.
Hope this helps....
Roger