Also referred to as a unique identification marking (UIM) in the WHO FCTC Protocol to Eliminate Illicit Trade in Tobacco Products. A unique identifier, in the context of excise goods traceability, is a serial number, assigned by a central authority for application to unit packages of excise products for the purpose of track and trace. No two serial numbers are the same, thereby allowing for the identification of individual retail-saleable items throughout the supply chain.