What are the markups for such symbols?
You can use
$\geq$ (to get $\geq$) or for a variant
(to get $\geqslant$).
For less than or equal to replace the "g" by "l".
For the strict versions, $\gt$ and $\lt$, you can use
or just the symbols
$<$. The symbols did sometimes create issues but I think this is fixed by now.
For a general guide see MathJax basic tutorial and quick reference