Certilogo Trademark Property of Certilogo.

TL • DR  I foot the bill for industry-leading authentication services for every piece that carries my signature.
Authenticate your piece at www.certilogo.com when it arrives, and keep the tag!  The tag is your key to ongoing verification if you decide to resell or trade the piece later.  If a reseller doesn't offer a valid Certilogo Seal of Authenticity, don't buy my work from them. 
No seal? No deal.  It's that simple.

Certilogo provides two simple authentication methods for my work:
 The first method is designed for buyers.  If you have a piece in front of you, scan the QR code on the tag, or enter the CLG number into the Certilogo app or website.  Answer a couple quick questions and the AI will let you know immediately if the piece is genuine.  If it turns out to be a fake, Certilogo records the event and offers you documentary support for fraud claims, charge backs, or refund requests.
The second method is designed for sellers.  After verifying that a piece is genuine, the seller can swipe left in the Certilogo app or on the website, and request a Seal of Authenticity.  The request is reviewed by Certilogo and an image of the seal is emailed to the seller within one business day.  The seal image can be included in an online listing, and allows online buyers to verify that the seller has the authentic product in hand.  After the sale, the buyer can then scan the tag to verify that the seller sent them the genuine article.
If you want more information about how Certilogo works or how to use it, they have a great FAQ that covers everything in detail.

If authentication is so easy, why aren't more brands protecting their customers from getting ripped off? 

The dirty little secret of streetwear is that counterfeiting helps drive the hype machine. Even when a collector knows they're wearing a knock-off and doesn't care, their fake piece still puts a logo or a cut out on the street, and that builds brand recognition.  For brands built on nothing but hype, a decent fake is almost as good as the real thing.
Sounds weird, but it's true.  Forcing collectors to publicly hook up on social media just to find out if pieces are genuine is a quick way to build emotional investment and to keep collectors talking about a brand.  Refusing to offer a centralized authentication system allows brands to manipulate consumer uncertainty.  That uncertainty generates "social proof" in the form of legit checks and fake-spotting guides, and that user generated content hypes the brand.  It's a sleazy way to build consumer engagement and give brand communities something to talk about when they don't have much else in common.
Think about this:  Every time you see a legit check or a conversation about how to spot a fake, you're actually looking at a free ad for that brand, created by collectors.  The impact of this kind of social proof is even greater when a piece publicly fails a check, because when something is seen to be worth counterfeiting, then the genuine article appears to be more valuable.  Likewise, when somebody out there has developed the expertise required to spot a fake, then fakes must be worth spotting, right?  That check-and-answer loop exploits basic human psychology and helps to drive sales and maintain brand awareness.
Bottom line, brands that don't offer centralized product verification are making a choice.  They're choosing to dump the responsibility of spotting fakes into your lap, which forces you to help them advertise.  They're choosing to increase the reach of their brand by disrespecting your time, exposing you to scammers, and putting you at risk of having your cash diverted into the global bootleg industry.
Frankly, I think that's a pretty shitty way to play this game, so I choose not to do business that way.