Short equals sign

graphicx allows for resizing things through \resizebox{<width>}{<height>}{<stuff>}. Here's what you could do:

\documentclass{article}
\usepackage{graphicx}% http://ctan.org/pkg/graphicx
\makeatletter
\newcommand{\shorteq}{%
  \settowidth{\@tempdima}{-}% Width of hyphen
  \resizebox{\@tempdima}{\height}{=}%
}
\makeatother
\begin{document}
Here is a~-~hyphen, here is a~\shorteq~sign.\par
Here is a~-~hyphen, here is a~=~sign.
\end{document}

The above MWE provides \shorteq that squishes a = into the width of - of the prevailing font.

---

textcomp also provides \textdblhyphen which is similar, but different:

\documentclass{article}
\usepackage{textcomp}% http://ctan.org/pkg/textcomp
\begin{document}
Here is a~-~hyphen, here is a~\textdblhyphen~sign.\par
Here is a~-~hyphen, here is a~=~sign.
\end{document}

You can define your symbol using two rules:

\documentclass{article}

\newcommand\textequal{%
 \rule[.4ex]{4pt}{0.4pt}\llap{\rule[.7ex]{4pt}{0.4pt}}}

\begin{document}

text~\textequal~text

\end{document}

If You have access to Unicode fonts you could also try U+FE66 (﹦) SMALL EQUALS SIGN compare (=|﹦) (In the fonts used by my browser in this web site SMALL EQUALS looks bigger than EQUALS, but mathematical typography isn't the strongest point about stackexchange:-)