What package does this symbol come from?

Question

What package does this symbol come from? I've tried Detexify without success.

Answer 1

the font in question is definitively (a modified) "english script". here is an image showing a sample that includes the E.

the design of "english script" was originally from linotype. the source of the font from which the OP posted the example was bitstream's "English157BT-Regular"; it was modified by unslanting it along with some minor editing. (most "wedding scripts" are much too severely sloped to be suitable for math use. "english script" is one of the more upright scripts, but even it is sub-optimal in its original form.)

i obtained this information from the person responsible for the font system at informs, the publisher of the operations research journal in which the symbol was found.

Answer 2

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{calligra}
\begin{document}

\textcalligra{E}

\end{document}

See http://www.tug.dk/FontCatalogue/calligraphicalfonts.html

Although possible, the font is not suitable for math scripts. This is the test code for math:

\documentclass{article}
\usepackage[T1]{fontenc}
\DeclareFontFamily{T1}{mcalligra}{}
\DeclareFontShape{T1}{mcalligra}{m}{n}{<-> s * callig15}{}
\DeclareSymbolFont{calligra}{T1}{mcalligra}{m}{n}
\DeclareSymbolFontAlphabet{\mathscr}{calligra}
\begin{document}

$x \in \mathscr{E}$

\end{document}