Mono-Signature

"Mono-signature" is an unusual phrasing for what most people call single-sig: one private key, one signature, controlling one output. It's the default Bitcoin spending pattern.

The vast majority of on-chain Bitcoin transactions today are single-sig: single-key output types account for roughly nine in ten of the inputs spent in a typical month (counting Taproot key-path spends, which look the same on-chain whether one key or an aggregate of several produced the signature), and script spends such as classical multisig are only a few percent. Multisig and aggregated schemes are used for higher-security custody (vaults, exchange cold storage, treasuries) or for protocol reasons (Lightning channels are 2-of-2 multisig under the hood; a 2-of-2 built with MuSig2 on Taproot can spend through the key path and look exactly like single-sig).

Schnorr (Taproot) single-sig signatures are a fixed 64 bytes; ECDSA signatures run up to 72 bytes in DER encoding, or 71 once a wallet grinds for low-R values. Both authorize spending with one private key, both look on-chain like one signature, both have the same single-point-of-failure security profile.

The tradeoff is the obvious one: one key, one point of failure. Lose access to the key (lost seed, dead drive, no backup) and the coins are gone. Compromise the key (malware, supply-chain attack on a wallet, careless seed handling) and the coins are stolen. Multisig and aggregated signatures spread that risk across multiple keys or devices, at the cost of operational complexity.

For most users, a single hardware wallet (single-sig) with a properly verified seed backup is dramatically more secure than the alternatives they'd actually execute correctly. Multisig is a real upgrade only if you're willing to use it competently.