Watch List notes:

IONIA. Uncertain mint. Circa 650-600 BC. Hemistater (Electrum, 17 mm, 8.74 g), Samian-Euboic standard. Rough plain surface. Rev. Bipartite incuse square. Unpublished, and one of only four or five examples known. The same reverse die was used on comparable staters, as CNG MBS 73, 2006, 339 and Triton VIII, 2005, 438. An extraordinary coin! With its blank 'obverse' and punched reverse, it stands at the dawn of coinage: between a pure ingot and an actual coin. Nearly as made.
From the Acer Rubrum Collection, ex Triton VIII, 11 January 2005, 439.

While the obverse is basically patternless, the reverse punch pattern is extremely unusual. The relatively small-sized punches, without any internal form, and their tight grouping is not found on other issues, and, presumably, reflects techniques used by metal refiners rather than actual minters. The possible attribution to Samos given in its previous auction appearance is highly tenuous, and probably unlikely .