Ultra sound money is an Ethereum meme focusing on the likely decrease of the ETH supply. If capped-supply gold is sound, decreasing-supply ether is ultra sound.

The ETH supply decreases whenever more ETH is destroyed via fee burn than ETH is created via issuance. Fee burn is a scarcity engine fuelled by Ethereum's transactional utility.

Fee burn is a mechanism which destroys ETH base fees paid for transaction inclusion on Ethereum. Fee burn started August 5, 2021 with the activation of EIP-1559.

Base fees are protocol-quoted minimum fees for transaction inclusion in an Ethereum block. Priority fees paid in addition to base fees are not burned.

The merge (see EIP-3675) is the hot-swapping of issuance-heavy PoW for issuance-light PoS. The merge will cause an issuance shock called the triple halvening.

The triple halvening is an issuance cliff roughly equivalent to three Bitcoin halvenings. At the merge total issuance drops from ~15K ETH/day to ~1.5K ETH/day.

Aug 2020—Vitalik Buterin jokes about supersonic money Sep 2020—Justin Drake memes about ultrasound money Mar 2021—Bankless popularizes ultra sound money

The bat signal is a visual expression of the ultra sound money meme, a playful nod to bat ultrasounds. The ultra sound fam wears the bat signal to spread the meme.