Names Over Players Head

How would this be done?
I use .\Shadow} Deathrun gamemode and have modifying it in the such:

Custom HUD
Custom Leaderboard
Custom Death/Player Models
Custom Sounds

I know how to do all that, but how do I make a rounded box over a players head that EVERYONE see’s that says something like ADMIN.
Would a plugin do this or do I have to customize the gamemode?
If so how and what file do I edit?

-Thanks the Lua Noob-