Party UI Combat Icons Guide
I noticed in this PvP video that he had several unusual icons over his head as well his party members heads showed icons also. I realized that these were the skill icons of the skills the players were performing at the time. So I went out to figure out these icons and how to configure them. I found that in the UI options there are several options to turn these icons on for not only seeing the icons over your own head but to see those icons of your party members as well. (They are off by default.) These come in quite handy for PvP as well as PvE. They indicate not only what skills are being used but information such as if someone has pulled aggro, a monster has enraged, someone has just taken a large percentage of their health in damage, or if someone is at low health. Below is a list of the different icons and their meanings.
Incidentally I also found a method to view someones health, level, as well as buffs with out engaging them in combat. Very useful in PvP situations where you need to gauge someones strength. I found that if you bring up the target marking HUD(the default key for this is Q on your keyboard) while the person is in your target reticle and then while holding q rather than selecting one of the marking icons you click in the center of the HUD. This will acquire the person in your target window and give you all relevant information. You can see the target marker HUD below.
On a side note I am the the huge Amani Lancer in in that pvp video at about 1:20 i come bumbling thru as Kinkybear.