I've no idea if this has been suggested but I thought it was a good idea.
Have the same conditions for spawning the marks but instead of spawning the mark itself have a placeholder NPC equivalent spawn for a limited time. Say 5-10mins? Once this NPC is clicked by anyone or a party it will spawn the actual mark itself for that person or party in an instance so it can be fought at their leisure.
Notorious Monster camping in XI was never fun from my experience and it's XIV equivalent isn't either. I really hope the developers take this into consideration.
Like this post if you think its a good idea.