Looking for a disjoint symbol

Question

Does anyone know how to make this symbol? Detexify couldn't help.

| o

The vertical line is centered on the 'o' and starts at the top of the 'o'.

Answer 1

Is this what you want?

\documentclass{article}
\usepackage{amsmath,pict2e}

\makeatletter
\newcommand{\disjoint}{}% for safety
\DeclareRobustCommand{\disjoint}{%
  \mathrel{%
    \mathpalette\disjoint@\relax
  }%
}

\newcommand{\disjoint@}[2]{%
  \begingroup
  \setlength{\unitlength}{\disjoint@height{#1}}%
  \begin{picture}(1.4,2)
  \roundcap
  \linethickness{\disjoint@thickness{#1}}
  \put(0.7,0.5){\circle{1}}
  \Line(0.7,1)(0.7,2)
  \end{picture}%
  \endgroup
}
\newcommand{\disjoint@height}[1]{%
  0.8\fontdimen5
  \ifx#1\displaystyle\textfont\else
  \ifx#1\textstyle\textfont\else
  \ifx#1\scriptstyle\scriptfont\else
  \scriptscriptfont\fi\fi\fi 3
}
\newcommand{\disjoint@thickness}[1]{%
  \fontdimen8
  \ifx#1\displaystyle\textfont\else
  \ifx#1\textstyle\textfont\else
  \ifx#1\scriptstyle\scriptfont\else
  \scriptscriptfont\fi\fi\fi 3
}
\makeatother

\begin{document}

\fboxsep=0pt\fbox{$\disjoint$}

$A\disjoint B$ 
$\scriptstyle A\disjoint B$
$\scriptscriptstyle A\disjoint B$

\end{document}

Answer 2

As @Noone pointed out, there is a similar unicode character (U+2AF0). As for most unicode characters, it is included in the STIX font. It can be accessed without loading the whole font as in the following example.

\documentclass{article}
\DeclareFontEncoding{LS1}{}{}
\DeclareFontSubstitution{LS1}{stix}{m}{n}
\DeclareSymbolFont{symbols4}{LS1}{stixbb}{m}{it}
\DeclareMathSymbol{\midcir}{\mathrel}{symbols4}{"BE}
\begin{document}
\( \midcir \)
\end{document}

Answer 3

There's a VERTICAL LINE WITH CIRCLE BELOW (U+2AF0) Unicode character and you can access to it via XeLaTeX or LuaLaTeX with a proper font:

\documentclass{standalone}
\usepackage{unicode-math}
\setmathfont{XITS Math}
\begin{document}
$⫰$ {\Large $⫰$} {\Huge $⫰$}
\end{document}

Answer 4

Using the \multimap symbol...rotated using also scalerel package.

\documentclass[12pt]{article}
\usepackage{amsmath,amssymb}
\usepackage{graphicx}
\newcommand{\circmap}{\raisebox{.7\depth}{$\rotmap$}}
\newcommand{\rotmap}{\rotatebox[origin=c]{-90}{$\multimap$}}
\usepackage{scalerel}
\usepackage{parskip}

\begin{document}
Euler's formula is remarkable: $e^{i\pi} + 1 = 0$.

But if I have two sets with $A \mathbin{\scaleobj{.7}{\circmap}} B$ we can write $A_{\scalebox{.5}{$\scriptscriptstyle \circmap$}}^{\scalebox{.5}{$\scriptscriptstyle \circmap$}}$

\end{document}

Or another alternative can be to use fontawesome5 with the command \faNeuter.

\documentclass[12pt]{article}
\usepackage{amsmath,amssymb}
\usepackage{fontawesome5}
\usepackage{graphicx}
\newcommand{\circmap}{\raisebox{.6\depth}{$\rotmap$}}
\newcommand{\rotmap}{\rotatebox[origin=c]{180}{\faNeuter}}
\usepackage{scalerel}

\begin{document}
Le be $\circmap$ a map: we define
\[\circmap \colon A \to B\] 
if 
\[A_{\scalebox{.5}{$\scriptscriptstyle \circmap$}}B\]

\end{document}