\documentclass[11pt,a4paper]{article}

\usepackage{marginalia}
\marginaliasetup{
  xsep=5mm, style=\raggedright\sffamily,
}

\usepackage{tikz}
\newcommand\drawarrow{%
  \tikz[remember picture,overlay]
    \draw[->,thick] (arrowstart) -- ++(-1.5mm,0) |- (.5mm,.5ex);%
}
\newcommand\savearrowstart{%
  \tikz[remember picture,overlay] \coordinate (arrowstart) at (-.5mm,.5ex);%
}

\begin{document}

Lorem ipsum dolor sit amet,%
\marginalia[mark={~$\triangleleft$}]{A marginal  note. (Extra text to push down the
  note below.)} consectetur adipiscing elit, sed do eiusmod tempor incididunt ut
labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation
ullamco laboris nisi ut aliquip ex ea commodo consequat.%
\marginalia[mark={\drawarrow}]{\savearrowstart Another  marginal note.}
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu
fugiat nulla pariatur.

\end{document}

