If I understand your question correctly, you need to choose the appropriate symbol (upper right corner, the "x" symbol) and then tap on the location you wish to indicate as "no go" (as that's what that symbol means, in-game). The mark dissapears after a short time. You can press on the mini map after selecting the symbol, if you're away from the location you wish to point out.
IGN: Aquiday
Main(s): Ardan, Koshka
Secondary: Catherine
Region: South America
Karma level: 13
Wins: 100+
Tier: The Hotness
VaingloryFire is the place to find the perfect build guide to take your game to the next level. Learn how to play a new hero, or fine tune your favorite VG hero’s build and strategy.
Splintermaster
Notable (1)
Posts: 43
Main(s): Ardan, Koshka
Secondary: Catherine
Region: South America
Karma level: 13
Wins: 100+
Tier: The Hotness
"I am the Crucible and the Flare..."
Aquiday
Notable (3)
Posts: 45
Splintermaster
Notable (1)
Posts: 43