They look exactly the same to me. Down to the brushes included in the set, the brush roll, and even where the company's name is stamped.

I fellow Makeup Addict messaged them about it, after she found the same brushes on BoldnTrendy and they replied with this:

"Thank you for your email and we appreciate your honesty as a customer. I want you to know that the brushes that you show here from Bold n Trendy are not Sigma brushes. There are many brush kits out there that try to mimic our style and quality but have not proved to do so. What I can tell you is that when purchasing from Sigma Beauty, you are guaranteed high quality products and exceptional customer care. All of our products have a one year guarantee and we are happy to help you any time that you need us. We stand behind our products and believe that we have the highest quality at the best price. If you have any other questions or concerns, please let me know and I will happily help you out.
Best Regards,
[Name of person who replied to me]"

*shrugs* it sounds more like "Oh, sh*t. Well, you found us mass-producing brushes. But guess what. We will tell you that these are NOT Sigma brushes...becaaause...uh...OH. Because they don't have SIGMA stamped on them. Yeah. But...uh...you will probably never find out if they are exactly the same, because you will not order from both of us, right? HAHAHA, we fooled you!"

Hmmmm... what do you think?