As a Sigma owner (Japanese DR28-12, 1982) who has been watching this thread forever, it's a bit sad to see that this whole page is Guests, who obviously haven't bothered to read back to the informational stuff.

Believe me, it's worth doing.

So, Guests, whoever you may be. Your Sigma is worth whatever you can persuade the market to pay for it. No-one here is qualified or can can be arsed to give you a valuation. If you read back the thread, you should be able to get a county of origin and might, just might, be able to get a date for it. Japanese-made ones are the cream, really early Japanese ones are the creme de la creme. Otherwise it's up to you to spin the story in your sales pitch.

Stories of interesting or rare variations (viz, the MoP headstocks) are that; interesting. We'd all love to know the full story, but it doesn't look like we ever will.

Anyone yet bought/tried/played a New Sigma? That would be a really interesting contribution...