What font is used for "Mathematica" in our logo?
I thought it might be the italic of the default Mathematica font (Utopia)—
—and while it looks similar, the logo font has angled vertical strokes on M, a serif at the top of c, a wider hook at the bottom of t, and a thicker horizontal stroke weight.
I tried some online font identification tools but they didn't work.
It seems to use a third font.
Jin mentioned in chat during the design phase that the font used in mma.se's logo is Vollkorn, with a custom kerning.
Currently, and since about Mathematica version 6/7, the main Wolfram Mathematica logo is set in Minion Pro Regular/Italic. Before then, a number of different fonts were used, including Palatino, some kind of all-capitals Garamond, Meridien, and, going back to version 1 (1989), Times Italic. To see some of the earlier versions of Mathematica's branding, visit the Wolfram Scrapbook.
In the following picture, first is the OP's original scan, followed by a redrawing showing what Palatino would look like. Then there's this site's font, Vollkorn. And finally, a redrawing using Minion Pro. The Palatino Italic is a bit more like handwriting.
Manipulate one day!