Perhaps writing to Sigma directly would help in the queries, e.g. if they'll honor warranty-servicing for lenses purchased out Singapore.
When I wrote Sigma (Singapore) a few weeks ago, this is what they said:
support <support@apds.com.sg> wrote:
>
> Dear Sir
>
> Yes you will be entitled to limited warranty if you can produce the
> international warranty card and purchase receipt.
>
> Regards
> Sigma Marketing (Singapore) Pte Ltd
>
>
> -----Original Message-----
> Sent: Friday, July 18, 2008 10:06 AM
> To:
support@apds.com.sg
> Subject: Query on lens warranty
>
> Hi,
>
> I am keen on purchasing the Sigma AF 150mm f/2.8 APO EX HSM macro DG D
> lens online from a Hong Kong-based seller. Can I inquire does Sigma
> include international warranty in this lens, as I hope for this lens
> to be shipped and then used in Singapore?
>
> Thanks!