How to make text in the game that only marines will see it ?

The only way i can think of it would be a big trigger_presence for the marines, initally switched off and targeting a game_text entity. If you want to display the text, enable the presence trigger, now every marine inside the trigger will see the message.
Dont know if it will work, it is just my theory. If you want the message to be seen by every marine arount the map, you would have to cover the whole map with you trigger_presence.