Watch List notes:

ASIA MINOR, Uncertain. 6th-5th centuries BC. AR Tetartemorion (6.5mm, 0.24 g). Head of horse right / Rough incuse square. Unpublished in the standard references. VF, some porosity, light scuff on reverse.

The horse head / incuse type is a fairly common fraction, but none of the published examples (cf., e.g., Klein 332) closely matches the style of this piece.