Backwards-z symbol

Adjust sizes at your will:

\documentclass{scrartcl}
\usepackage{mathtools,pict2e}

\newcommand*\ztimes
  {\DOTSB\mathbin{\mathpalette\ztimesaux\relax}}

\newlength\ztimespadding
\setlength\ztimespadding{.3ex}

\newcommand*\ztimesaux[2]{\vcenter{\hbox{\hspace{\ztimespadding}%
  \ifx#1\displaystyle
%   \setlengnth\ztimespadding{.3ex}%
    \setlength\unitlength{1ex}%
    \linethickness{.1ex}%
  \else\ifx#1\textstyle
%   \setlengnth\ztimespadding{.3ex}%
    \setlength\unitlength{1ex}%
    \linethickness{.1ex}%
  \else\ifx#1\scriptstyle
%   \setlengnth\ztimespadding{.3ex}%
    \setlength\unitlength{.8ex}%
    \linethickness{.09ex}%
  \else\ifx#1\scriptscriptstyle
%   \setlengnth\ztimespadding{.3ex}%
    \setlength\unitlength{.65ex}%
    \linethickness{.07ex}%
  \fi\fi\fi\fi
  \begin{picture}(1,1)\roundcap
    \put(0,0){\line(1,0){1}}
    \put(1,0){\line(-1,1){1}}
    \put(0,1){\line(1,0){1}}
  \end{picture}%
  \hspace{\ztimespadding}%
}}}

\begin{document}
$A \ztimes B = C_{A \ztimes B = C_{A \ztimes B}}$\par
${\times}{\ztimes}_{{\times}{\ztimes}_{{\times}{\ztimes}}}$
\end{document}

A mirrored version of the lowercase z, upright and with a sans-serif font, which scales appropriately:

\documentclass{article}
\usepackage{graphicx}
\usepackage{amstext}
\newcommand*{\backwardsz}{%
  \text{\reflectbox{$\mathsf{z}$}}%
}
\begin{document}
\[
  A\backwardsz B_{\backwardsz_\backwardsz}
\]
\end{document}