Hi Rupert,
I cannot tell if it's appropiate or not, but if you do decide to mark it with the RASC red/green square on the tank sides here are some pictures of my original ones!
Definitely a Greek marking "Σ450" and a crown. Have seen such markings on quite a lot of motorcycles of different brands.
Attached a picture from a 3HW with such a marking....
Kostas
Hello, my name is Kostas, I'm from Athens Greece.
Studied architecture and trying to make a living out of it!
Proud owner of two Norton WD16Hs thus I have joined this forum.
I hope you'll all be a friendly and helpful bunch :-D
Cheers,