Trust Guards are The Trust security personnel, in The Conduit. They wear Mk13 "Avenger" body armor, which is similar to that of the Puppet Humans, except for that the Guards' armor is blue, albeit with few differences. Even though the game's mutiplayer mode describes them as being Trust security personnel, they are never seen inside The Trust Base.
The armor that they wear can be used as a multiplayer skin. This skin is simply called Guard. Its colors are customizable for primary being the chest and helmet, along with other parts with the outside armor, and the secondary colors are the visor and spaces in between.