The Orange PI zero is equipped with two onboard leds ,

 

One red , and one green ,
armbian give you the ability to control very easily the state of theses leds.

to turn on the red led you can use this command : echo 1 > /sys/class/leds/red_led/brightness
to turn off the red led you can simply launch : echo 0 > /sys/class/leds/red_led/brightness

to turn on the green led you can use this command : echo 1 > /sys/class/leds/green_led/brightness
to turn off the green led you can simply launch : echo 0 > /sys/class/leds/green_led/brightness

You can put some sleep command between the on and off, and use this functionality to notify you for example that a cron script is running.