Alfred Ralphs offers Greek Septuagint version of Genesis 4:15 that mentions the "mark" or "sign" of Cain.
Alfred Ralphs, ed., Septuaginta: With morphology (electronic ed.) (Stuttgart, Germany: Deutsche Bibelgesellschaft, 1979), Genesis 4:15, accessed December 21, 2022
καὶ ἔθετο κύριος ὁ θεὸς σημεῗον τῷ Καιν τοῦ μὴ ἀνελεῗν αὐτὸν πάντα τὸν εὑρίσκοντα αὐτόν
And the Lord God set a mark/sign upon Cain that no one that found him might slay him.