While @Simply a Christian has provided a fine answer to this question, there is one more wrinkle that can be added for the sake of completeness.

We know of a tradition of supplying the Tetragram (Y-H-W-H), HaShem, the name of God, in special characters from the Dead Sea Scrolls. One of the clearest places to see this is in the [Psalms scroll from Cave 11][1]:

![11QPs'a'][2]

Or, in close-up:

![Tetragram][3]

In this scroll, the Name is consistently written in [paleo-Hebrew script][4], showing the special status accorded to it.

Something like this also happens in Greek transmission. In an influential article,<sup>1</sup> Albert Pietersma drew attention to [Origen][3a]'s knowledge of this phenomenon in Septuagint mss:

> In the more accurate exemplars [of the LXX] the (divine) name is written in Hebrew characters; not, however, in the current script, but in the most ancient.

Pietersma goes on to note the evidence of the *pipi* texts, that is ΠΙΠΙ in Greek - *pi* + *iota* + *pi* + *iota*, which appears to be Greek scribes reproducing in ignorance the letters of the Tetragram, יהוה, but in Greek characters rather than Hebrew. That is, the two *he* letters (ה) represented by *pi* (Π), the *yod* and *vav* (ו ,י being virtually identical in, e.g., the Hebrew script of the Dead Sea Scrolls -- or Arial, for that matter) both represented by *iota* (Ι). Obviously in this scenario the letters used for the Tetragram are most likely to be standard "square" script (i.e., not paleo-Hebrew) in an otherwise Greek setting. 

I don't know if this is what lies behind OP's information that LXX contained "יהוה transliterated", but it's possible. Origen's testimony suggests that something like this practice was known to him.

---

*Note*

1. A. Pietersma, "[Kyrios or Tetragram: A Renewed Quest for the Original LXX][5]", in *DE SEPTUAGINTA. Studies in Honour of John William Wevers on his sixty-fifth birthday*. Ed. by Albert Pietersma and Claude Cox (Benben Publications: Mississauga, 1984), pp. 85-101. What follows is cited from pp. 87-88 - see the PDF for discussion and references.


  [3a]: http://plato.stanford.edu/entries/origen/#OriLifWor


  [1]: http://www.deadseascrolls.org.il/explore-the-archive/image/B-314640?locale=en_US
  [2]: https://i.sstatic.net/TAnqo.jpg "Just three occurences of the paleo-Hebrew Tetragram are circled - there are more in this picture."
  [3]: https://i.sstatic.net/fYXUQ.png "Close-up : see link to www.deadseascrolls.org.il to see full manuscript."
  [4]: https://en.wikipedia.org/wiki/Paleo-Hebrew_alphabet
  [5]: http://homes.chass.utoronto.ca/~pietersm/KyriosorTetragram%281984%29.pdf