'X' and 3-2-1 above party member's head

[tyhlin]

How do you do this?

 

The other day I was in a party and one member had a huge X above his head, in the same fashion as when party member numbers are displayed above players' heads. Then another party member started a countdown before we started fighting a boss.

[Elvenmad]

 party markers, check in your game settings > key bindings > Emblems         it shows you the bindings

[Teffy]

CTRL+1