Any eth*/web3 wallet that supports NFT's (and thus supports arbitrary 'web sourced' transactions, such as the approve() message and the transfer() methods) supports signing messages. eg: metamask. This is a non issue for the NFT holders. The https://github.com/walletlink/walletlink standard appears to be what a lot of 'stand alone' type wallets are using for this compatibility.

If the client doesn't support arbitrary transactions (eg: it is a 'receive and spend ether' only type wallet), its probably not interacting with NFT contracts in the first place.

I still don't understand. My coinbase wallet has collectables, but no way to prove ownership of the collectable. If I can't take a challenge from anyone a spit out a signed response without downloading/installing additional software it kinda defeats the whole purpose no?

> If someone sells an nft claiming ownership of someone else's intellectual property

NFTs don't transfer ownership though. This isn't like theft. You're basically making a certificate of authenticity and selling just the certificate. I don't have any idea how courts would interpret that.

What NFT claims is kind of blurred. Ianal, but it will take a real.life test to confirm 'stealing' of anything in counterfeit NFTs case in court.