The Mexican hallmark is the system of official marks applied to precious metal articles in Mexico to indicate fineness, maker, locality and assay. Mexican hallmarking has run continuously, with reform, since the colonial period, and a piece of Mexican silver or gold can carry marks from any of three principal eras: the colonial assayer system from roughly 1539 to 1821, the post-independence interregnum of inconsistent regional marking, and the modern federal system from 1948 to the present.

The colonial system used a small letter M surmounted by a crown for Mexico City, with a separate assayer's initial and a fineness number expressed in dineros for silver. Other locality marks identified Guadalajara, Puebla and other provincial assay offices. These marks are the subject of detailed reference works in the museum literature and are essential for dating and authenticating colonial silver.

The federal eagle mark, often called the aguila, was introduced in 1948 and required on all manufactured silver. It consists of an eagle head in profile within a numbered cartouche, the number indicating the city or assay office. Eagle one corresponds to Mexico City, eagle three to Taxco, and so on through the regional centres. The eagle mark was discontinued in 1979 and superseded by an alphanumeric system that remains in force.

Under the current system, a Mexican silver piece typically carries three marks: a fineness mark such as .925 or 950, a two-letter alphabetic code identifying the city, and a numeric maker registration. The two-letter code begins with the locality letter, for example TA for Taxco or OA for Oaxaca, followed by a sequential maker number assigned by the Direccion General de Normas. The system is administered by the Secretaria de Economia under Norma Oficial Mexicana standards, and the marks are registered in a public database.

Gold marking in Mexico follows the same alphanumeric structure with a karat fineness substituted for the silver standard. Articles in 14k carry the 0.585 mark, 18k the 0.750 mark, and so on. Imported precious metal articles are marked with the importer's registration in addition to any foreign maker marks.

For the dealer or appraiser, the practical guidance is straightforward. A piece bearing the eagle is necessarily between 1948 and 1979. A piece with the alphanumeric code without an eagle is from 1979 or later. A colonial mark requires consultation with the specialist literature and, ideally, with a Mexican silver hallmark reference such as Anderson or Mejer. Unmarked Mexican-style silver is common in the tourist market and carries no formal guarantee of fineness.