I've had trouble in the past sending LION batteries overseas as well. The US Postal Service has strict guidelines on how you can ship them. After May 16th this year, forget it with the USPS unless you meet certain shipping criteria which is a pain in the butt...including special handling packages and certification.
If you lie and say something like "computer parts" or something on the claims form, and it is discovered during xray
(which happens too much
) then they automatically confiscate the battery and place it in a bin for disposal. You lose everything.
Even UPS requires a "dangerous goods" form to be followed, and they have a great algorhythm to help you determine if you need one or not. Check out this pdf:
http://www.ups.com/media/news/en/pack_batteries.pdf
From what I read, the Sig III has a 1500mAh battery at 7.4V DC. This works out to
(1500*7.4
)/1000=11.1Wh. By UPS standard here in the US, by the weight and everything, the battery would not need a "dangerous handling/goods" document and should be able to be shipped without problem.
Maybe your best option would be to have the Sig III shipped to someone you know in the US and then have them UPS ship it overseas to you...though I have no idea what shipping costs would be.
Also FedEx is supposed to be another good option, but again, I have no idea the rates. But whatever you do...forget using the US Postal Service....arrrgh!!!