The LED-resistor across the breaker with the anode end connected to the Main Bus, and the cathode connected to the load-end is commonly done. Pick the resistor to limit the LED current (with the breaker open) to ~10mA, and use an ultra-bright RED led. At 10mA, they are bright enough to be noticeable even in sunlight. If the load has an ON/OFF switch (say a Transponder), and the switch is turned off, then the LED will not light even if the breaker is tripped. There is a work around for this; parallel the load with a 1K resistor.