In Masechet Shabbat 104a, it talks about the shapes of the letters, and meaning behind it. One thing it says is: ומאי טעמא שיקרא אחדא כרעיה קאי ואמת מלבן לבוניה? And what is the reason that ...
In Shabbos 77a-77b, Chazal ask about the spelling of a series of words, questioning whether the words are spelled with an alef - as in גראינין - or with an ayin - as in גרעינין. Wasn't ayin vocalized ...