I know we're all too familiar on the Elder-Futhark Runes, or just runes in general. Type of sigils that can propose a divinatory meaning, when asking a specific question. Runes can be made of anything: bones, pieces of wood, or carved into stones that help draw an accurate answer to your question. Your runes are in a bag, and once you ask a question (while invoking some sort of deity if necessary), draw a rune from the bag, and there's your answer. Correct me if I'm wrong, please (because I'm not that great on Norse-y things).
Greek Alphabet is almost like the same thing. Except, it's a little different, with a few different options. The first method uses pottery. Be aware that some of the letters look the same from different angles so you might need a little help on how to determine which one differs from the other. Example: Mu (M) differs from Epsilon. Here's what that looks like since the chatter won't let me post the actual letter: http://tinyurl.com/pd4esy9
For those who aren't aware what these letters look like, here is for your convenience and future reference: http://tinyurl.com/o3qfn7s
Not to be confused, I know there are some characters on there that seem different. Such as: Tau and Tao are different spellings, but they are the same. Khi and Chi are the same, pronounced the same as well.
There is a second and third method used for casting.
The second one, involving 24 pieces of knuckle bones and the third involving five dice (I will elaborate the second and third methods for those with continuing interest in this).
The runes themselves have a broad meaning, and the same goes for the letters of the Greek alphabet. These meanings that go with these letters do not have a ''reversed'' meaning. So what you get, is what you get, and it's up to you and your intuition to how it applies to you and your life and/or current situation.
The Greek alphabet, for those who are interested and don't already know, basically goes: Alpha (Alfa) , Beta (Vita), Gamma (Yhamma), Delta, Epsilon, Zeta, Eta, Theta, Iota (Yoh-ta), Kappa, Lambda Lamtha), Mu (Mi), Nu (Ni), Xi, Omicron, Pi, Rho, Sigma, Tau (Taf), Upsilon (not to be confused with Epsilon, Eep-silon), Phi (fee) Khi, Psi, and Omega. In the parethesis are the phonetics, and how to pronounce the letter.
Main source: https://web.eecs.utk.edu/~mclennan/BA/GAO.html
Like I previously stated, all of these letters have their own specific meaning and answer. Normally with the Greek letters, your answer is your answer. It's only up to you to decide whether it's positive, negative, or what it means to you.
I'd be happy to elaborate more on the subject in a future time.
Just to supplement your original post, a couple of excellent books about divination and oracles in Ancient Greece are Mantike: Studies in Ancient Divination edited by Sarah Iles Johnston and Peter T. Struck, and Ancient Greek Divination by Sarah Iles Johnston.
