[Tex/LaTex] Label equation with a symbol

Question

I would like to label an equation with an arbitrary symbol, rather than a number, or letter. Is this possible?

Answer 1

Perhaps something like this.

\documentclass[11pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}   % loads »amsmath«

\begin{document}
  \begin{equation}\label{eqn:einstein}
    E=mc^2\tag{*}
  \end{equation}
  \eqref{eqn:einstein}
\end{document}