https://www.pcgamer.com/see-fortnites-new-ping-system-in-action/

The Fortnite Season 8 patch notes detail volcanic vents, cannons, and a pretty new UI, but this season's most prominent new feature is Fortnite's new ping system. Taking a cue from how we and everyone else have fawned over Apex Legends' deep, intuitive communication tools, Epic's implemented its own simpler take on team comms for Fortnite. 

A single ping that isn't focused on an object spits out a location marker, marked by a blue arrow on the screen, also visible on the map. A quick double-tap turns that icon red to indicate the enemy's position. For all markers, if the marked position or item isn't visible in your immediate field of vision, it'll turn into an icon on the edge of the screen closest to the marked position.