1. the beginning of some form of of οἰωνός “omen”
2. genitive plural of οἶς, meaning “of sheep”
3. a genitive plural of some other word with a stem ending in -οι-, but with the beginning of the word missing. For example, the demonstrative τοίων “of such”, relative οἵων “of which”, or ποίων “of a certain kind”. Or, as speculated in the article, ὁμοίων “same”.
The 3rd option seems most likely to me without any further context. ὁμοίων seems especially plausible since the preceding characters do resemble "ΟΜ".
The image is annotated OIWN and the article tentatively identifies the word as OMOIWN, meaning "similar".
"Wine-dark sea is a traditional English translation of oînops póntos (οἶνοψ πόντος, IPA: /ôi̯.nops pón.tos/), from oînos (οἶνος, "wine") + óps (ὄψ, "eye; face"), a Homeric epithet. A literal translation is "wine-face sea" (wine-faced, wine-eyed). It is attested five times in the Iliad and twelve times in the Odyssey[1] often to describe rough, stormy seas. The only other use of oînops in the works of Homer is for oxen, for which is it used once in the Iliad and once in the Odyssey, where it describes a reddish colour. The phrase has become a common example when talking about the use of colour in ancient Greek texts."
