Euripides, Theseus fr. 382 (Nauck)
An illiterate herdsman spells out Theseus’ name, which he has seen written on a ship.
ἐγὼ πέφυκα γραμμάτων μὲν οὐκ ἴδρις,
μορφὰς δὲ λέξω καὶ σαφῆ τεκμήρια.
κύκλος τις ὡς τόρνοισιν ἐκμετρούμενος,
οὗτος δ’ ἔχει σημεῖον ἐν μέσῳ σαφές·
τὸ δεύτερον δὲ πρῶτα μὲν γραμμαὶ δύο,
ταύτας διείργει δ’ ἐν μέσαις ἄλλη μία·
τρίτον δὲ βόστρυχός τις ὣς εἱλιγμένος·
τὸ δ’ αὖ τέταρτον ἡ μὲν εἰς ὀρθὸν μία,
λοξαὶ δ’ ἐπ’ αὐτῆς τρεῖς κατεστηριγμέναι
εἰσίν· τὸ πέμπτον δ’ οὐκ ἐν εὐμαρεῖ φράσαι·
γραμμαὶ γάρ εἰσιν ἑκ διεστώτων δύο,
αὗται δὲ συντρέχουσιν εἰς μίαν βάσιν·
τὸ λοίσθιον δὲ τῷ τρίτῳ προσεμφερές.
I’m not knowledgeable about letters, but I’ll tell you their shapes and give clear tokens. A circle, like one measured out with compasses, and it has in its middle a clear mark. The second is first two lines, and another one holds them apart at their middles. The third is like a curly lock of hair, and then the fourth has one line standing straight up, and three more fixed across it. The fifth is not easy to describe; for there are two lines which begin apart, and they run together into a single base. The last one resembles the third.
= ΘΗΣΕΥΣ. The third and final letters which the herdsman describes are of course the curly ‘lunate’ form of sigma: C.