\documentclass{scrartcl}
\makeatletter
\def\theindex{%    only for demonstration
  \section*{\indexname}
  \parskip\z@ \@plus .3\p@\relax \parindent\z@
  \let\item\@idxitem}
\makeatother
%StartVisiblePreamble
\usepackage{makeidx}\makeindex
%StopVisiblePreamble
\pagestyle{empty}
\begin{document}
\section{Escaping characters with >}
\begin{itemize}
\item Exclamation mark ! \index{exclaim (>!)}
\item Vertical bar| \index{Vertical bar (>|)}
\item Doublequote \verb|"| \index{>"}
\item Double doublequote \verb|""| \index{>">"}
\item At character @ \index{At (>@)}
\end{itemize}
Run \texttt{xindex} with \texttt{xindex -e ">"}\index{<file.idx>}\index{123}
\newpage
\printindex
\end{document}
