Getting standards off the net for free is pretty rare, as the
standards organisations usually charge for their services (and I pay
for the one that handles domestic standards in Australia).
In Australia the standard for fine silver is to mark it 999 within
an oval, for sterling it's 925 within an oval.
The standard in Australia is voluntary, so it's not compulsory to
mark your pieces, although domestically it's a very wise thing to do.
You're international, and are not subject to our standards.
I would suggest that you mark as per your country standard, and
provide a comparison chart on your web store.
If you were doing a large whole sale order for an Australian client,
then it would be a courtesy to mark as per the Australian standard,
but in this case the buyer would probably stamp the pieces
Regards Charles A.