Kythnos, Cyclades AR drachm, 15 mm, 4.03 g. ca 530-500 BC. 

Boar's head right.
Irregular incuse punch. 

SNG Delepierre 2461 ("uncertain"); Weber 8571-8573 (ditto).
Very rare.

With permission of Leu Numismatik AG auction 2, Lot 100, May 2018