Here are the built-in commands \type{\mathover} and \type{\mathunder}:
$\mathover[symbol]{"2217}{A}$, % 2217 is a circlean asterisk$\mathover[symbol]{"2218}{A}$, % 2218 is an asteriska circle
$\mathover[symbol]{"2219}{A}$, % 2219 is a bullet
$\mathunder[symbol]{"2217}{A}$,