Sidetic script

From the longer Wikipedia page 
The Sidetic language is a member of the extinct Anatolian branch of the Indo-European language family known from legends of coins dating to the period of approximately the 5th to 3rd centuries BCE found in Side at the Pamphylian coast, and two Greek–Sidetic bilingual inscriptions from the 3rd and 2nd centuries BCE respectively. The Greek historian Arrian in his Anabasis Alexandri (mid-2nd century CE) mentions the existence of a peculiar indigenous language in the city of Side. Sidetic was probably closely related to Lydian, Carian and Lycian.
The Sidetic script is an alphabet of the Anatolian group. It has 25 letters, only a few of which are clearly derived from Greek. It is analysed from coin legends in what is possibly Sidetic. The script is essentially undeciphered.
More details, including a list of inscriptions, on the Wikipedia page.
Category:Undeciphered writing systems