The Agents from the Matrix were sort of the inspiration for these characters, with a few modifications of my own. All I can tell you is "Don't expect them all to be in MIB suits."
And they aren't all smiling. You can see that Agent Thomson gets more and more pissed off as Agent Samuels cheerfully ribs him.
Except that their mouths are in "smiling" position in all panels. It makes for some odd contrast with their actual actions.