% !TeX TXS-program:compile = txs:///pdflatex

\documentclass[margin=5mm]{standalone}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}[line cap=rect]
	\draw[very thick] (0,0) grid (3,3) ;
	\foreach \Pos in {(1.5,2.5),(0.5,1.5),(2.5,0.5)} \draw \Pos node[font=\LARGE] {$\heartsuit$} ;
\end{tikzpicture}

\end{document}