I was taking a look at Wikipedia's page on the Ryukyuan languages when I came across the following picture:
The billboard on the left features three kana-like characters that I have never seen before, and that are not part of the gojuuon system. Interestingly, they are not listed on Wikipedia's page for Okinawan scripts either, despite this page detailing four different transcription systems (Conventional, Council, Ryukyu University, and New Okinawan).
Given that the caption below this picture says that it was taken in the town of Kin, I presume that the sign is written in a Kunigami language variety? However, I can't seem to find any references that describe a unique kana system for this area. Would anyone be able to provide any references that list the readings for these characters (and any others that may be in use for this language variety)? Thanks!