Bourbaki assembly brackets

BONUS: Works across math styles

\documentclass[12pt]{article}
\usepackage{ulem,scalerel,rotating}
\newcommand\bkl{\mathopen{\stretchrel*{\rotatebox{90}{\uwave{\rule{3ex}{0pt}}}}{Xy}}}
\newcommand\bkr{\mathclose{\stretchrel*{\rotatebox{90}{\uwave{\rule{3ex}{0pt}}}}{Xy}}}
\begin{document}
$A \bkl x, y \bkr.$
\end{document}

Width could be tweaked a little with this:

\documentclass[12pt]{article}
\usepackage{ulem,scalerel,rotating}
\newcommand\bkl{\mathopen{%
  \stretchrel*[180]{\mkern-1mu\rotatebox{90}{\uwave{\rule{3ex}{0pt}}}}{Xy}}}
\newcommand\bkr{\mathclose{%
  \stretchrel*[180]{\mkern-1mu\rotatebox{90}{\uwave{\rule{3ex}{0pt}}}}{Xy}}}
\begin{document}
$A \bkl x, y \bkr.$

$\scriptstyle A \bkl x, y \bkr.$

$\scriptscriptstyle A \bkl x, y \bkr.$
\end{document}

The stix package has ⧘ \lvzigzag and ⧙ \rvzigzag, which resemble the image you posted and may even be semantically the same. These two characters are encoded in Unicode as LEFT WIGGLY FENCE (U+29D8) and RIGHT WIGGLY FENCE (U+29D9).

So, you can either use

\documentclass{article}
\usepackage{stix}

\begin{document}
$A \rvzigzag x, y \lvzigzag$
\end{document}

or, with Unicode support, you need a font that supports ⧘ and ⧙ such as STIX2Math:

\documentclass{article}

\usepackage{unicode-math}
\setmathfont{STIX2Math.otf}

\begin{document}
$A ⧙ x, y ⧘$
\end{document}

Sorry, I totally don’t understand the use of both characters, so their use and the notation may be completely wrong in my example.