RS-232 Tx / Rx monitoring LEDs?

[dwight]

I was going to add something but it has already been
said several times.
I will add that if using a LED on an AC like signal of high voltage,
one should use a diode.
I recommend using a shunt diode rather than a series diode when
high voltages are being dropped by the resistor. It reduces the need
for a high voltage diode but makes the resistor hotter.
Some red LEDs glow orange when not protected from 12VAC.
You can ask how I know.
Dwight