Thanks for the continuing input Guys and I appreciate the interest.
On first seeing the pin I felt that it most certainly referred to a maritime squadron, probably operating flying boats. However, this belied the information that the pilot in question had flown both Spitfires and Mustangs whilst serving with 129 Squadron.
Looking into the squadron’s war time history I notice that in 1943 it was tasked with carrying out maritime operations, including both interdiction of surface ships and escorting fleet convoys.
The Mustang was more suitable than the Spitfire for this role as it had a longer range and carried more suitable firepower.
Whilst unfortunately I have been unable to find any direct reference to the badge I am also certain that it would have been worn by those pilots flying the Mustang and tasked with maritime ops.
Later in the war the squadron reverted back solely to the Spitfire and its original fighter role.
Of course this is mostly conjecture, so I continue to search for a more definitive answer...