The cup was discovered at Pithekoussai, an ancient Greek site on the island of Ischia just off the western coats of Italy near Naples – one of the earliest Greek colonies in Italy. Decorated in a typical geometric pattern in black slip, with symmetric lines, shapes and patterns, it's the three-line inscription which is most interesting. The text, dating to 740 to 720 BCE, appears to have been written very shortly after the alphabet was introduced to Greece by trade contact with Phoenicia (the modern Levant) – and it also appears to be one of the first ever literary references, to Homer's Iliad.
The text runs like this (given first in classical orthography, and then in English translation):
Νέστορος [....] εὔποτ[ον] ποτήριο[ν]·
ὃς δ’ ἂν τοῦδε π[ίησι] ποτηρί[ου] αὐτίκα κῆνον
ἵμερ[ος αἱρ]ήσει καλλιστ[εφάν]ου Ἀφροδίτης.
(?) Nestor’s cup, good to drink from.
Whoever drinks from this cup, him straightaway
the desire of beautiful-crowned Aphrodite will seize.
The literary reference revolves around the description of Nestor's cup, mentioned in the Iliad book 11, lines 632-637. In a sense there's a joke being made here: while the cup of Nestor described in Homer is a fabulously costly object, made of gold with four decorated handles, this is a simple two-handled clay drinking cup. It's been suggested that the lines may have been written as part of a sympotic drinking game, where attendants at the symposium had to alternate taking turns in composing a line of hexameter poetry each. To me, however, the most suggestive thing about it is that our earliest evidence of writing in Greek contains both a high-flung reference to Homeric poetry, an appeal to Aphrodite (in the style of Sappho), and a joke: a wonderfully suggestive nod to the richness of the Greek textual tradition and its ability to survey all the different registers of human experience.