The lower part of the fork leg, half covered by the side of the mudguard. They'll either be Ti Nitride (gold coloured) or normal chrome plated. Ducati UK should be able to tell you the specifics from the VIN number. Either mail them or call them.
Quote them the frame number and they should be able to unequivocally tell you what it is, when it was imported, etc.
It's been a gripe of mine for a long time that the government show things like "Ducati Two Wheeled Motorcycle" on log books. It just gives free reign to unscrupulous types to allow them to pass-off one model as being another (not that I'm implying that's necessarily the case here).
Phoned Ducati and they confirmed that everything was ok. They didnt seem concerned that they had written the frame number down incorrectly in the warranty book either!!
Have phone DVLA and Datatag and everything is now sweet.