LEDs need about 2V to turn on. You can't expect to put 2V across them and expect them to work, ESPECIALLY if you've also got a resistor in series. You'll need to add some gain.
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Actually, it's not clear what you are trying to do here. If you are just trying to light an LED when a +/- signal is present, just put a two resistors, two LEDs and and some protection diodes. You may not even need the protection diodes, depending on the reverse voltage rating of the LEDs.