Nothing I hate more than seeing a grown man whine...
It's completely possible that SHIELD existed during Gulf War 1, but it didn't have any emblems. In all likelihood, it probably started as a clandestine black-ops unit primarily engaged in back-office work -- tracing money laundering that funded the Soviets, looking into Communist paper trails, maybe doing psi-ops work, undercover missions. That's certainly the impression I get from the "you, me, and a bar tab" comment.
Thus, I don't see any reason why SHIELD ought to have a formal insignia, or for its operatives to display a symbol identifying them as part of an espionage unit. (That's why, it's, like, espionage. Duh.)
It would make sense that SHIELD only underwent expansion in the wake of the attacks on New York City and Washington. Basically, not long after the resoltion to form the Ultimates was passed, the Trisk' was commissioned, and the Homeland Security Department was established. I doubt they needed any formal insignia, prior to those events.