In defence of tanks (I am one after all, except when I'm not, in which case I'm a hooker) if I see that sign there then I know I have to explain the dungeon layout, any moves from the boss, let's take Stone Vigil.

New player message you explain about giant dragon coming down and making Lalakebob so don't fight there else you'll burn!
First boss, when it runs, stand behind it, it'll special, turn then special again so avoid it.
Then you talk them through what is ahead in the rest of the dungeon.

When I was going through AK the first time I had an annoying healer who was about as helpful as a chocolate fire guard, I didn't know which mobs to tag in which order, they were less than helpful so I buggered off. 2nd time with a group of JP players, the DRG marked the order, talked through boss fights (where to stand) the wall fight (where to stand, where not to stand etc.) and my first proper run was a win and a win for me as I now know the order for when I go through with friends.