So I can reassure all who believe because of your brushes Made in China is that it is automatically a fake. That's just plain wrong. Sigma has some time ago already changed his style of brush, because just had a lot of fakes on the market.
Therefore, no longer stands on the USA brushes for the number. Earlier rear stand PRC on which, moreover, is nothing more than Made in China (Peoples Republic of China). To mention just a few facts. Look, for example, but the pictures on the homepage at Sigma. There you will also no longer behind the USA brush number.
There are some other changes that have been made. The "new" brush are so since last year in circulation. Who's command of English will find much more. Some authorized dealers of Sigma have even provided explanations with pictures online to the changes. Give Just Sigma Made in China as a search term. And do not go crazy.