\documentclass[11pt,twoside]{letter}
\pagenumbering{gobble}

\usepackage{lmodern}
\usepackage{carlletter}

\usepackage[dvipsnames]{xcolor}
\usepackage{circledsteps}
% status pills: \TODO, \TODO{text}, likewise \FIXME and \DONE
\usepackage{xparse} % for the optional {text} argument
\usepackage{xspace}
\NewDocumentCommand{\pill}{m m m g}{%
    \CircledParamOpts{inner color=#1, outer color=#2, fill color=#2}{1}{%
        \textbf{#3}\IfValueT{#4}{ \textbf{--} #4}%
    }%
    \IfNoValueT{#4}{\xspace}% keep the space in "\TODO bla"
}
\newcommand{\DONE}{\pill{black}{LimeGreen}{DONE}}
\newcommand{\TODO}{\pill{black}{Goldenrod}{TODO}}
\newcommand{\FIXME}{\pill{white}{Red}{FIXME}}

\usepackage{graphicx}
\graphicspath{{img/}}

\usepackage[autostyle]{csquotes}
\MakeOuterQuote{"}

\begin{document}

Vincent Lannurien \\
64 rue Paul Masson \\
29200 Brest

\begin{flushright}
    À l'attention de ...
\end{flushright}

\begin{flushright}
    le , à, \\
\end{flushright}

\vspace{40px}

Madame, Monsieur,

\vspace{20px}

...

\vspace{40px}

\begin{flushright}
    Vincent Lannurien

    \vspace{20px}

    \includegraphics[width=4cm]{signature.png}
\end{flushright}
\end{document}