What does SIA mean, in Pontiac Firebird SIA?

[Gopher & Kit]

So my friend and I are trying to figure out what SIA stands for on my car, its a 1992 Pontiac Firebird and it has the intials SIA on the side of the car, i'm a teenager so I don't know much about the types of cars i'm still learning but I've made the intials to stand for her name which is Sadie Isabella Adrianna but i would like to know what SIA actually stands for..can anyone help me? nobody in my family and none of my friends know

 

[Goatman]

Doesent sound like it was put on from the factory I would think somone has put it on for some reason or another ..
I have never seen those letters on any firebird or T/A..