Notice the [size=9]
8-bit[/h] text at the bottom, that is exactly what I'm trying to put in my signature; as you're seeing, my sig has the standard font.
Note: The section above is
directly copy and pasted from my signature.
I've tried other custom fonts, and no custom fonts work. Effects work though (e.g. [#color=poop], [#b], [#u] and other standard effects).
Try this little experiment for me: Add [#text=kongtext]poop[/font] to the bottom of your signature (remove "#"), and tell me if it works.