I can’t find the LaTeX command for the symbol below. Can anyone help me out to find this symbol? I wasn't able to find it with Detexify.

I can’t find the LaTeX command for the symbol below. Can anyone help me out to find this symbol? I wasn't able to find it with Detexify.

Depending on your usage, the following may suffice:

\documentclass{article}
\usepackage{graphicx}% http://ctan.org/pkg/graphicx
\newcommand{\crosseq}{\mathrel{\ooalign{$\neq$\cr\reflectbox{$\neq$}\cr}}}
\begin{document}
$f(x) = g(x) \neq h(x) \crosseq i(x)$
\end{document}
The symbol \crosseq consists of an overlay of \neq and a reflected \neq. For a short lesson in \ooalign and symbol overlaying, see \subseteq + \circ as a single symbol (“open subset”).
graphicx package? Did you copy it correctly? What "[is] not working"?
– Werner
Aug 07 '13 at 07:52
graphicx) and compiling under pdflatex. Note that \crosseq can only be used in math mode. Are you getting an error or a warning?
– Werner
Aug 07 '13 at 08:11
Well here is one that looks kinda like cheating, it uses amsmath only, though adding calc will make the definition much simpler:
\documentclass{article}
\usepackage{amsmath}
\newlength{\crossl}
\settowidth{\crossl}{$\times$}
\newlength{\ceql}
\settowidth{\ceql}{$\times=$}
\addtolength{\ceql}{-\crossl}
\newcommand{\crosseq}{\mathrel{\makebox[\crossl][l]{$\times\hspace{-\ceql}=$}}}
\begin{document}
$f(x)\crosseq g(x)\crosseq h(x)$
\end{document}
Result:

One can also play around with the position and the symbols used:
\newcommand{\crosseq}{\mathrel{\makebox[7.7778pt][l]{$\neq$\hspace{-6.7778pt}\raisebox{-2.5pt}{$\backslash$}}}}

EDIT: Since this answer is chose I will add some more solution, this time using egreg's suggestion as poking around with boxes will likely create unexpected spacing issue:
\newcommand{\crosseq}{\mathrel{\ooalign{\hidewidth$/$\hidewidth\cr\ooalign{\hidewidth$\backslash$\hidewidth\cr$=$\cr}\cr}}}
or
\newcommand{\crosseq}{\mathrel{\ooalign{\hidewidth$/$\hidewidth\cr\ooalign{\hidewidth\raisebox{-2pt}{$\backslash$}\hidewidth\cr$=$\cr}\cr}}}
Result:

EDIT2: Add [l] option to \makebox in order to adjust alignment.
\DeclareMathOperator? I'd say it's a \mathrel. However, \mathrel{\ooalign{\hidewidth$\times$\hidewidth\cr$=$\cr}} is simpler.
– egreg
Aug 07 '13 at 08:47
Just for a change, no \ooalign:
\documentclass{article}
\usepackage{amsmath}
\usepackage{graphicx,calc}
% make \widthof usable with \hspace
% http://tex.stackexchange.com/a/99242
\makeatletter
\def\@hspace#1{\begingroup\setlength\dimen@{#1}\hskip\dimen@\endgroup}
\makeatother
\newcommand{\rnot}{%
\mathrel{%
\text{%
\makebox[0pt][l]{%
\hspace{\widthof{$=$}}\reflectbox{$\not$}%
}%
}%
}%
}
\newcommand{\crosseq}{\rnot\not=}
\begin{document}
$a\crosseq b$
\end{document}

xcancel as the cross is vertically centred on the = sign
– Chris H
Aug 07 '13 at 09:24
You might consider using the cancel package. Its command \xcancel places a cross over any given symbol. For a relation symbol like = you should enclose the whole construct in \mathrel to get the correct horizontal spacing:

\documentclass{article}
\usepackage{cancel}
\newcommand{\cancelledeq}{\mathrel{\xcancel{=}}}
\begin{document}
\( a = b \cancelledeq c \)
\end{document}
Poor man's code (simplified and stolen from egreg's):
\documentclass{article}
\usepackage{mathtools}
\usepackage{graphicx}
%
\newcommand{\crosseq}{%
\mathrel{%
\text{%
{$\neq$\reflectbox{$\not$}}%
}%
}%
}
\begin{document}
$a\crosseq b$
\end{document}

on the theory that there was some meaning to the asymmetry of the original drawing, and stealing egreg's very nice name for the symbol, here's another approach.
\documentclass{article}
\usepackage{mathtools}
\usepackage{amssymb}
\newcommand{\crosseq}{\mathrlap{{}\mathrel{\smallsetminus}{}}\not=}
\begin{document}
$a\crosseq b$
\end{document}
