There definitely are others - I think ABQ and ATL come to mind where I’ve seen locals refer to the area/city by that same code.
Chloe’s right about SFO though :)
Oh yea I think I've heard that about ATL before, but didn't know about ABQ!
I think I've said "SF" a grand total of like 4 times, and I 100% agree that if someone said "SFO" I would in no way assume they mean the city