Ρυνδα[- -] is clear in the top line, and there is a second line with a trace of a diagonal of either Χ̣ or retrograde Σ̣. Rhynda- is the beginning of either a personal name or potamonym. This graffito was published by Jury Vinogradov in Arkheolohiia (1994.2) pp. 146-147, with proposed reading Ῥύνδα[ξ] or Ῥύνδα[κος] (SEG 44.653, ca. 550-525 BC), and he also drew attention (pp. 144-148) to an honorific inscription from Olbia Pontica ca. 100-50 BCE (IOSPE I² 207, SEG 44.656) where the city of Ἀπολλωνιᾶται πρὸς Ῥύνδακον (Apollonia ad Rhyndacum) is mentioned (see https://pleiades.stoa.org/places/511151). Outside the Northern Black Sea region, there are attestations of the name Rhyndax in Attica in the IV century (IG II² 9096; SEG 24:223; SEG 35:134); and in Euboea (IG XII,9 978). I am inlined to see a personal name derived from the potamonym in our graffito.

Ῥύνδακος was the ancient Greek name of the river on the border between Mysia and Bithynia; today it is called Mustafakemalpaşa river, a tributary of Simav river, which flows into the Sea of Marmara. At least two ancient settlements are known in epigraphic sources as located near the river Ῥύνδακος: Ἀρταίο τεῖχος ἐπὶ το͂ι Ῥύνδακι is listed in Athenian Tribute Lists (IG I³ 71, Col. III, line 115, 425/4 B.C.E. and IG I³ 77, Col. IV, lines 4-5, 422/1 B.C.E.). Besides the above mentioned inscription from Olbia, the demos of Ἀπολλωνιᾶται πρὸς Ῥύνδακον is attested honouring the city of Miletos (Milet I 3, 155); the city also features in several inscriptions of the Roman period.