In philately a cancellation that does not contain the locale where it was applied is called a mute cancel. It seems to me that that could apply to such medals as well.

Anonymous. A numismatic or medallic item in which the creator – engraver, designer, sculptor, or minter – is unknown; an unsigned item. Anonymous is applied to items without initials, monogram or signature, precluding immediate identification of its maker. Sometimes anonymous items can be identified by documentary research, as by STYLISTIC COMPARISON with known items by the same artist (where the artist used the same mannerisms in several of his works). Often published or unpublished lists of an artist's work are the most productive sources for identifying anonymous works. See ART HISTORY.

A study of 19th century American tokens and medals revealed that 80 percent of these items were anonymous. We know the names of hundreds of early American engravers, but the custom – or practice – was for these engravers not to sign their dies.

Thus anonymous numismatic items are legion throughout history, both American and foreign. Many factors preclude an artist from signing his work: an embarrassment, by order of the issuer, or publisher, or government, or employer; or the fact the piece just does not justify a signature in the mind of the artist. An early anonymous medal is a Lucrezia Borgia Medal of 1502. See SIGNATURE.

The term "anonymous" is applied to artists only. If the portrait on a coin or medal is unknown it is termed: unknown subject and a catalog description might read "portrait of an unknown subject (or setter)."

References: CLASS 03.6 N2 {1958} Babelon, p 31.