Symbol for "care of" (c/o)

\documentclass[a5paper]{article}
\newcommand{\co}{%
  \leavevmode
  \begingroup
  \setbox 2 = \hbox {\small c}%
  \setbox 0 = \hbox {/}%
  \dimen 0 = \ht 0  \advance \dimen 0 by -\ht 2
  \raise \dimen 0 \box 2
  \kern -0.3333\wd0/\kern -0.3333\wd 0
  \lower \dp 0 \hbox {\small o}%
  \endgroup
}
\begin{document}
\co\space Mr. Bean
\end{document}

Probably quick and dirty, see ISO character entities and their LaTeX equivalents on page 3:

${^c\!/\!_o}$ Jim Jones

---

Edit: Included suggestion from Tobi’s comment having the letters c and o non-italicised:

$\mathrm{^c\!/\!_o}$ Jim Jones

The "c" should be level with ascenders and the "o" at the baseline; with textcomp's \textfractionsolidus the slash is slightly better than the normal /; but for symmetry it can be slightly raised up.

\documentclass{article}
\usepackage{textcomp}
\makeatletter
\newcommand{\co}{%
  \check@mathfonts
  \raisebox{.85ex}{\fontsize{\sf@size}{\z@}\selectfont c}%
  \kern-.1em\raisebox{.2ex}{\textfractionsolidus}\kern-.1em
  {\fontsize{\sf@size}{\z@}\selectfont o}%
}
\makeatother
\begin{document}
\co\ Mr.~Bean

\end{document}