What is the code of this square symbol?

Question

Recently, I encounter this square symbol. Although I search carefully on the Internet, I could not figure out its syntax.

Please help me find its syntax!

Answer 1

You can use Zapf Dingbats through the pifont package features.

\documentclass{article}
\usepackage{pifont}

\newcommand{\unnamedsymbol}{\ding{113}}

\begin{document}

\unnamedsymbol

\end{document}

There is a similar one at slot 111

If you want to use it as a math symbol, here analogous to the Alembertian,

\documentclass{article}
\usepackage{pifont}

\newcommand{\unnamedsymbol}{\mathop{{}\mathding{113}}\nolimits}
\makeatletter
\newcommand{\mathding}[1]{\mathpalette\math@ding{#1}}
\newcommand{\math@ding}[2]{%
  \begingroup
  \mbox{\normalfont\fontsize{%
    \ifx#1\displaystyle\f@size\else
    \ifx#1\textstyle\f@size\else
    \ifx#1\scriptstyle\sf@size\else
    \ssf@size\fi\fi\fi}{0}\selectfont
    \ding{#2}%
  }%
  \endgroup
}
\makeatother

\begin{document}

$\unnamedsymbol F_{\unnamedsymbol F}$

\end{document}