Twitter founder and billionaire Jack Dorsey is selling his — and the world’s — first tweet as a non-fungible token (or NFT), with the current highest bidder offering $2.5 million for the missive.

Dorsey launched the sale Friday, March 5th, tweeting out a link to the platform, Valuables. The site allows people to sell one-of-a-kind digital certificates of specific tweets, which are “autographed” and verified by the original sender. The current highest bidder for Dorsey’s inaugural tweet — which reads simply, “just setting up my twttr” — is Bridge Oracle CEO Sina Estavi.

As to why anyone would pay to own a tweet, Valuables states in an FAQ page: “Owning any digital content can be a financial investment, hold sentimental value, and create a relationship between collector and creator. Like an autograph on a baseball card, the NFT itself is the creator’s autograph on the content, making it scarce, unique, and valuable.”

NFTs are an increasingly popular element of the ever-growing world of cryptocurrency. Essentially, they can turn anything digital — tweets, Gifs, videos, art, songs — into a collectible or asset. Like Bitcoin and other cryptocurrencies, NFTs are sold and bought via the blockchain, a transparent digital ledger to track the item’s movement; as Vasja Veber, CEO of a start-up called Viberate recently explained to Rolling Stone, NFTs “cannot be copied and are easily tradable.”

In the music world, the interest in NFTs and cryptocurrencies has grown significantly, with many seeing an opportunity for artists to enhance revenue streams and engage with fans directly. In February, Grimes auctioned off 10 pieces of digital artwork as NFTs, while that same month, Portugal. the Man launched their own crypto coin, PTM Coin, which fans will eventually be able to spend on NFTs. And last Friday, March 5th, Kings of Leon became the first band to release an album as an NFT.