The day Tony Stark returns from Afghanistan, he holds a press conference. You can see Agent Coulson in the crowd.
I think no-one knows that Tony will become "Iron Man" at that time.
My question is when did S.H.I.E.L.D start to keep an eye on him?
Until that press meeting, Tony was just a businessman who created new weapons.
Was S.H.I.E.L.D following him for his weapons?