Circle over letter - LaTeX mathring command

The LaTeX command \mathring draws a circle over letters.

$\mathring{A}$ \\
$\mathring{ABC}$

The border and background of circle is black and white respectively. If you use accents package, the command \ring is an alternative to \mathring.

\documentclass{article}
\usepackage{accents}
\begin{document}

$\ring{A}$ \\
$\mathring{ABC}$

\end{document}

Various circles

The command \accentset in the accents package enables to write LaTeX circles on a letter.

\documentclass{article}
\usepackage{accents}
\begin{document}

\noindent
$\accentset{\circ}{A}$ \\~\\
$\accentset{\circ}{ABC}$ \\~\\
$\accentset{\bigcirc}{B}$ \\~\\
$\accentset{\bigodot}{C}$ \\~\\
$\accentset{\odot}{D}$

\end{document}