DPST power circuit w/ LEDs
simulate this circuit &ndash; Schematic created using CircuitLab

I couldn't find a NC/NO swith in the schematic editor, so consider the two pushbuttons as the two poles of your switch.

The resistor values should be adjusted to suit the power supply voltage - 1K is reasonable for 12 volts.  D1 will be on when the device is off, and D2 will be on when the device is on.