\documentclass{book}
\usepackage{marginnote}
\usepackage{graphicx}
\newcommand\Section[2][\reversemarginpar]{{%
#1%
\section*{\marginnote{\raisebox{-1.1\height}{\rotatebox{90}{#2}}}}}}
\begin{document}
\Section{Chapter 1}
Test Test Test
\newpage
\Section[]{Chapter 2}
Test Test Test
\end{document}