Data that is inscribed in a blockchain as a way to perpetuate the data, rather than to follow the main intended purpose of the given blockchain, e.g. ASCII art instead of financial transactions on the Bitcoin blockchain.
Namecoin examples are catalogued at: The are small Unicode art or emoji code.
There seems to be nothing of particular artistic value as far as we've seen so far, the only interest in such tokens seems to be that:
  • there are some examples that came earlier than those in the Bitcoin blockchain, notably a bit earlier than Section "BitLen"
  • Namecoin is a NFT system unlike Bitcoin which is fungible, so those assets are naturally tradable