I was running Sanguine with some random folks, and someone was marking the mobs. And they were marking them “instantly”. This wasn’t for bosses, just trash packs.
While all trash is created equal, some trash is more equal than others, and they deserve a 
and an 
.
So I had to assume that this was some kind of addon that “knew” which mobs in each dungeon were more deserving of random pug TLC than others.
Does anyone know what addon it might be?
Going to take a guess that it’s a weakaura.
It really does not take a addon.
Just bind a key and click them.
A macro also can be made.
Found this in the macro & UI
< title include “tank”.
/tm [@focus] 8
Set the target marker to be a skull.
See https://wowpedia.fandom.com/wiki/MACRO_targetmarker for an explanation of /tm and its marker #'s (0 to 8) since its a new command introduced with 9.0
Going to second this… I run M+ with a tank friend and his weak-aura auto-marks at least three trash targets as we’re clearing up to a boss.
I run with people who have this WA all the time but nobody seems to use the markers to communicate lol. What’s the point if people are just going to type out/say “I’ll sit big guy” or “interrupt on staghorns order me, shaman, war.”
You can configure which markers are used and who they are used on, but nobody explains the markers before-hand so I just assume they keep the default set-up unless they say otherwise. Still, it doesn’t matter, since I already know who I’m attacking and who I’m ccing when.
It mostly just puts a bunch of random icons on the screen 
The only important mark is skull, the rest is cereal