http://en.wikipedia.org/wiki/Tetragrammaton
http://en.wikipedia.org/wiki/Paleo-Hebrew_alphabet
Torah was given in the Ashuri script. The prove comes from Talmud (Mesechet Megillah 2b), which states that a miracle was needed to hold the letters ם (mem) and ס (samech) on the stone tablets. However, because of script's sanctity, it was not used for mundane writings, but kept in the Holy of Holies. A non-holy (and easier to write) Ivri script was adopted to the point where even the Torahs used for mass study were written in it. Eventually, the Ashuri script became forgotten by the common people, and was only preserved by the Sages. For this reason, only Daniel (a sage) could decipher the "writings on the wall" (Daniel 5:5 - 5:28), which appeared in the Ashuri script. After the Assyrian-Babylonian exile, the Ashuri script was reintroduced, and gained popularity even among the common people. According to the Talmud (Mesechet, Sanhendrin 22a) the name Ashuri comes from the fact that its an "upright" (מאושר) script, or because it became popular, when Jews returned from the Assyrian (אשור) exile. The Dead Sea Scrolls support Ritva's view, in that Ashuri is the holiest script. Most Qumran fragments were written in this script. In many cases, however, God's name (YHWH) appears to be referenced to by four dots, or is written in the Ivri script (see picture). The reason for this is related to the sanctity of the name of God in Jewish tradition. As soon as God's name is written in the Ashuri (holy) script, it requires extra care and more caution
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