I am looking for a way to encode this symbol:
This is the natural check mark for a left-handed person, as this is what happens when we apply an outward flick of the wrist to a pen. However, all the checkmarks I have found for LaTeX are right-handed.
Sure thing! Reflect the regular \checkmark (from amssymb) using graphicx's \reflectbox:
\documentclass{article}
\usepackage{amssymb,graphicx}
\newcommand{\lcheckmark}{\reflectbox{\checkmark}}
\begin{document}
\verb| \checkmark|: \checkmark \par
\verb|\lcheckmark|: \lcheckmark
\end{document}
For the sake of completeness, there also some others (right-handed) related symbols:
\documentclass{article}
\usepackage{bbding}
\usepackage{fontawesome}
\let\Cross\undefined % oooppsss...
\usepackage{marvosym}
\usepackage{wasysym}
\begin{document}\huge
\faCheck{ }
\faCheckCircle{ }
\faCheckCircleO{ }
\faCheckSquare{ }
\CheckmarkBold{ }
\Checkmark{ }
$\checked$
\CheckedBox{ }
\end{document}
But if you are tired of packages of symbols:
\documentclass{article}
\usepackage{graphicx}
\begin{document}\huge
\rotatebox[origin=c]{-120}{\sffamily 7} checked
\end{document}