This is a simple extension with the intent of improving provenance in ERC-721 tokens representing works of digital art.
As NFTs evolve further into representing digital art, there is a need to strengthen the link between a token and the digital work itself. With the current standard, a symbolic URI is the only information present linking the art to the blockchain. The URIs may become lost over time and the link may be lost. Hashing the digital art is a good link but pre-images may be lost. This standard focuses on allowing the artist to store a signature for each NFT, and allows the artist to designate an original and limited printed editions in a trustless way that does not rely entirely on the metadata.