You could have NPC's in set locations around the map that work like Watchers in Dota. You have to activate them with a heavy melee and afterwards, if they see an enemy hero in their area, they give an audio cue and brief vision on the map. To be honest, 90% of why I'd like to see this is so we can have buskers / shoe shiners / news paper boys that serve a purpose and add more flare to the map.