> (%i1) load("mactex-utilities")$
> (%i2) texput(signum,"\\sgn")$
> (%i3) tex(signum(x));
> $$\sgn\left(x\right)$$
I tried that, but the output of tex(signum(x)); is
$${\it \sgn}\left(x\right)$$
which then causes the rendered output to appear as "(x)".
-matt