Signers aren’t altruists—they are paid for the service they provide.
Signer fees should always be paid or escrowed up front. To achieve this, signer fees must be guaranteed by minting, and deposits must have predictable lifetimes.
A detailed treatment of signer fees can be found in its own section.
Fixed-term deposits mean signer fees can easily be calculated per deposit. A standard term of {term-length} means depositors can budget for fees, and signers will know how long their bonds will be inaccessible. To incentivize redemption at term, the system is structured such that deposits can only be redeemed by the owner of the deposit during the term, but anyone may redeem deposits once they reach term. Additionally, at-term redemptions still charge their signing fees from the deposit owner, unless fees have been escrowed by the vending machine.
Depositors that don’t need future access to their deposit might prefer to pass the costs of the system to eventual redeemers and/or want denomination beyond the BTC lot size or fungibility. These depositors can opt to receive a non-fungible Fee Rebate Token which pays a fee rebate at the time of a deposit’s (pre-term) redemption by another user. The rebate mechanism is explained further in the discussion around minting.
At the end of the deposit term, the deposit can be redeemed by anyone including the signers themselves, with signer fees owed by the deposit owner. This mechanism is discussed in more detail in the section on redemption.