Okey, so I will start of by saying that this system I will describe is a very usefull and popular system in at least one other MMO-RPG game.
What I noticed when doing trials is the lack of visability. You have a certain tactic, lets say you split into two groups and you need to always stay infront of your healer within that group. Either you need to know your group very well and know exactly where your healer will go. Or you will have to look at other characters and read their name and make sure you're infront of the healers name. This makes it a bit unclear during combat and especially if you pug.
Another thing that raid marks could and are used for is marking specific locations on the ground. If you have a tactic where someone in the group needs to go to a specific place at specific times it makes the whole experience a lot more pleasant if you as a raid/trial leader can mark that location so it's easy for that person to know exactly where to go.
The main thing with raid marks is to dump down the visual clutter. A way for your brain to easily sort which information is usefull and which isn't.
Here's an example of how it could look (in the example I choosed to show one raid mark on a player and one on the ground but the prefered amount of raid marks would need to be more than one.)
Edited by Jultzy on July 8, 2018 12:48PM
Jultzy Altmer Sorcerer (AD)
Narjiha Bosmer Nightblade (AD)
Jules Yaká Breton Sorcerer (DC)