I don't remember which glyph it came from but it is definitely obtainable since I can make it. I did know all the glyphs prepatch so my guess it that it came from either Books of Glyph Mastery or Northrend research. If it came from the books prepatch it can be obtain through the research now. They changed inscription so that the book glyphs can be learned either through the books or research. The books just make it faster.