TLDR: blockchain may be used to prevent counterfeit of physical goods by mirroring the supply chain. There is a serious challenge to this process though: if some consumers still accept product not verified on blockchain, a cheating supplier can sell them the authentic product and inject the counterfeit into blockchain-backed supply chain. However, if authenticity verification through blockchain is introduced for hi-tech cryptocurrency-related devices like hardware wallets, virtually all buyers will require blockchain verification from sellers, thus making the procedure effective.

General idea

The idea to use blockchain to prove authenticity of goods prone to counterfeit is not new [1][2]. Overall scheme is like this:

• Each product is represented by token on a blockchain with public ledger.
• Preferably, product should have unique ID, then token should have same ID.
• Every physical product transaction in supply chain is mirrored by blockchain transaction.
• If there is a blockchain transaction trail from manufacturer to you, it's a proof that you have authentic product.

The scheme seems solid. Blockchain is basically a guarantee of cryptocurrency authenticity, so it can work same way with physical goods, right?

The problem

Well, I see one problem similar to double spend. Nothing prevents a cheating supplier to replace authentic product with a fake copy. Then they can sell authentic product on black market to an expert who can determine authenticity reliably without blockchain. Also realistically, many consumers won't learn or won't care about blockchain verification.

For instance, imagine if Fender issued a token for each custom guitar. I could buy one guitar and get a token. Then I can order a cheap copy of the guitar and sell it on Ebay, backed by token. Even if the buyer complains, I have a proof of authenticity, so there is a good chance to win the dispute. Now I have authentic Fender for a price of a copy. I can play it by myself or sell it to my friend who trusts me or has witnessed everything. Even better, I can go and sell my authentic Fender to someone who doesn't know anything about new verification policy. I really doubt the manufacturer will write "please register" on the guitar itself.

As long as there is a consumer who doesn't need or know about the blockchain proof, they can be given the real product, and verified-on-blockchain product can be fake. They may participate in counterfeit wittingly or unwittingly, but the end result doesn't matter: the blockchain authenticity guarantee fails.

Products for which blockchain verification can work

To minimize effect of this weakness two conditions must be met:

1. Virtually every customer must know about blockchain proof of authenticity.
2. Virtually no customer must value blockchain-unverified product more than a fake.

The best kind of product to satisfy these conditions are hardware wallets. Everyone who uses them knows and cares about blockchain. If the manufacturers introduced their own token to verify device authenticity, virtually 100% of users would quickly learn the news and would avoid buying devices not backed by tokens.

Now, there is a valid argument that there are no fake Trezors and Ledgers manufactured today, and the biggest concern for buyers is getting a compromised device. (Note: you probably should download and flash official firmware on a new hardware wallet, even if it's shipped directly from the factory, just in case). Obviously, blockchain can't prevent tinkering, only a physical guard like a seal can help. But while blockchain verification can't prevent tinkering directly, it can serve as an evidence to identify and expose the tinkerer, possibly with legal consequences.

Sooner or later, there should appear fake Ledger or Trezor clones, and also more second hand authentic devices will be sold. Tokens on blockchain will help to distinguish authentic ones from the fakes.

Similarly to hardware wallets, authenticity of ASIC miners or any other blockhain-related devices can be secured by tokens. I can't recall any such devices except hardware wallets and miners, but there definitely will be more in future.