Indicators are mostly particle effects to indicate a position inside the world. This is a handler functionality and cannot directly be used.
It's implemented by the schematic builder and world edit light handler.

Note: The amount of particles being displayed is limited by the game. To many indicated coordinates will result in most of the particles being despawned before even seen. Depending on the indicator used this effect might be huge (e.g. particle or cross).

Not all indicators might be allowed for all implementations but this is a list of the ones which are provided by MCL:

Explosion (default)

Name:e or explosion
Method:particle # largeexplode


Name:p or particle
Method:particle # reddust


Name:c or cross
Method:particle # reddust


Name:b or barrier
Method:particle # barrier

Ender Crystal

Method:summon entity # EnderCrystal
Warning:These ender crystals will explode when hit! Use kill command to remove them or live with a big explosion. Not to be used under normal cirumstances (advantages bigger than a block and persistent).