Voltage divider/reduction with no current draw
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Opto-isolator current monitor.

As jsotola suggests, you can use an opto-isolator but rather than connect in parallel you can connect in series to reduce power consumption and save another series resistor. This will decrease the voltage available to your 12 V LED by about 1.4 V or so but this is unlikely to be an issue.

Notes:


The opto-isolator LED has to carry the full current for your existing LED.
R2 may be omitted if an internal pull-up is used. That makes it a single-component solution.


@Trevor's solution is simpler and cheaper. Use this one if isolation between the circuits is an advantage.