Normal subgroups

The same symbol is also available as \trianglelefteq from the amssymb package. It gives a much wider spacing.

\documentclass{article}
\usepackage{amssymb}
\begin{document}
$H\trianglelefteq G$
\end{document}

Appropriate math spacing for relational operators is obtained using \mathrel:

$H\mathrel{\unlhd}G$