Congratulations JJ,
I'm looking at ordering the same but was a bit concerned if Amazon were selling UK or EU stock so that I could get the Sigma 3yr warranty, the Amazon response didn't help:
"Hello,
I glad to hear that you wish to purchase "Sigma 150-500mm f5-6.3 APO DG OS HSM for Canon Digital and Film SLR Cameras" from us and certainly understand your concern.
All electronic items purchased from Amazon.co.uk come with a one year warranty from the manufacturer, unless otherwise stated.
We currently don't offer an extended warranty on the electronics items sold on our website. If the details on the Product Description page state that the item has a warranty greater than 12 months, then this warranty is with the manufacturer and not Amazon.co.uk. If you believe you are eligible under this warranty you'll need to contact the manufacturer directly.
I hope this helps. We look forward to seeing you again soon."
So not much help here, can you shed any light on this if you've registered with Sigma yet?
BB