The symbol on Aaron Turon's thesis title page

This one looks like adforn n° 21:

\documentclass{article}

\usepackage{adforn}

\begin{document}

\adforn{21}

\end{document}

You might also want to take a look at PGFOrnament and PSVectorian.

Just for fun, use @PhelypeOleinik nice answer for your work

You can indeed construct such a symbol from integral signs:

\documentclass{article}

\usepackage{graphicx}

\title{title}

\begin{document}

\maketitle

\begin{center}
\scalebox{2}{\rotatebox{-50}{$\int$}\kern-0.95em\rotatebox{-50}{$\int$}}
\end{center}

text

\end{document}