That crossed swords stamp is related to the Birmingham Proof House, it dates and identifies the inspector who did the proofing.
This link should clear it up on how to date the proof;
Proof Date Codes
Now it has the 'D' at right, I'm not 100% sure, but I think it indicates which series of years. Since letters can only denote 25 years ('I' wasn't used), I think the 'D' means 1997-2022 and I would hazard a guess that the 'F' denotes that the barrel was proofed in 2003. The '3' below is the inspector number.