Producing centered asterisk to indicate new section

Try this:

\documentclass[pagesize,fontsize=12pt,paper=a5,DIV=9]{scrartcl}
\usepackage{blindtext}
 \def\EndSection{\section*{\hfill*\hfill\hfill}}
\begin{document}
\blindtext\par

\EndSection

\blindtext
\end{document}

This is how I'd do it:

\documentclass{article}
\usepackage{kantlipsum}
\newcommand{\finishsection}[1][0]{%
  \ifhmode\unskip\fi % to emulate what \par does
  \ifnum#1>0 \enlargethispage*{#1\baselineskip}\fi
  \par\nopagebreak
  \vbox to 3\baselineskip{\centering
    \vss
    $*$\qquad$*$\qquad$*$\par
    \vss
  }
}
\addtolength{\textheight}{-7\baselineskip}
\begin{document}
\kant[1-3]
\finishsection
\kant[4-5]
\end{document}

If you change -7\baselineskip into -8\baselineskip the asterisks will be moved to the next page. In such a situation you can do

\finishsection[1]

that will execute \enlargethispage*{1\baselineskip}. Maybe an automatic version with needspace is feasible, but in quality book production I'd go for manual check.