Now that I have seen the photograph it certainly looks like a Harley Davidson. I have only ever had one motorcycle, which was a T20SH Triumph Tiger Cub.
Another sign board, I have covered a term that was in common use at the time in case it has repercussions.
If I am not mistaken about the location, Ernest Currill seems to have been on the Italian main land as well as on Sicily.
Cassino War Cemetery. Corporal Thomas Henry Boyce | War Casualty Details | CWGC Almost certainly known to Ernest Currill as Thomas Henry Boyce also came from Oxford.
These are both German 15 cm sFH 13/1 (Sf) auf Geschützwagen Lorraine Schlepper(f). You can find more information here: 15cm sFH 13-1 (Sf) auf GW Lorraine Schlepper(f) Basically a German 15 cm sFH 13/1 howitzer mounted on top of a captured French Army Lorraine 37L tracked armored transporter.
The aircraft is a Lockheed Hudson Lockheed Hudson - Wikipedia The vehicle partly visible on the left is probably a Thornycroft ‘Amazon’ Coles Crane? 1942 Thornycroft 'Amazon' Coles Crane - Yorkshire Air Museum
In the link there is an identical photograph to one of mine. It would seem that soldiers kept copies of the same photograph as souveniers, unless, of course it came from the same source, which is unlikely.