答案1
\documentclass{article}
\usepackage{amsmath,amssymb}
\newcommand{\AC}{%
\mathord{\vtop{%
\ialign{%
\hfil##\cr
$A$\cr
\noalign{\nointerlineskip}
$\scriptscriptstyle\mathbb{C}\mkern2mu$\cr
}%
}}%
}
\newcommand{\LC}{%
\mathord{\vtop{%
\ialign{%
\hfil##\cr
$L$\cr
\noalign{\nointerlineskip}
$\scriptscriptstyle\mathbb{C}\mkern2mu$\cr
}%
}}%
}
\newcommand{\MC}{%
\mathord{\vtop{%
\ialign{%
\hfil##\cr
$M$\cr
\noalign{\nointerlineskip}
$\scriptscriptstyle\mathbb{C}\mkern6mu$\cr
}%
}}%
}
\begin{document}
$\AC\quad \LC \quad \MC$
\end{document}
答案2
虽然 OP 指的是数学字母 A、L 和 M,但图像给人一种无衬线的印象。这是宏\subC[<fine adjustment>]{letter}
\documentclass{article}
\usepackage{txfonts,stackengine}
\newcommand\subC[2][0pt]{%
\ensurestackMath{\stackengine{-.03ex}{\mathsf{#2}\kern-\dimexpr#1\relax}{%
\scriptscriptstyle\varmathbb{C}}{U}{r}{F}{F}{S}\kern#1}%
}
\begin{document}
$\subC{A}\quad \subC{L}\quad \subC[.5pt]{M}$
\end{document}
适合普通衬线字母的版本:
\documentclass{article}
\usepackage{txfonts,stackengine}
\newcommand\subC[2][.3pt]{%
\ensurestackMath{\stackengine{-.03ex}{#2\kern-\dimexpr#1\relax}{%
\scriptscriptstyle\varmathbb{C}}{U}{r}{F}{F}{S}\kern#1}%
}
\begin{document}
$\subC{A}\quad \subC{L}\quad \subC[1.0pt]{M}$
\end{document}