What to do with an unsigned complaint letter?

An unsigned complaint letter should typically be treated with caution, as it lacks accountability and may not be taken as seriously as signed correspondence. It's advisable to acknowledge receipt of the letter but to inform the sender that without a signature, you cannot address their concerns formally. Encourage them to resubmit their complaint with a signature for proper handling. If the issues raised are significant, consider investigating them internally, but do so discreetly.