After all, private investigators usually don't advertise themselves as guns for hire. Also naming anything "Golden" is an obvious choice in a city created by the Gold Rush and defined by the Golden Gate.
But apparently there really was a Golden Gate Investigations. A little Googling revealed its address was more recently in another neighborhood. A little more Googling revealed that they are now out of business.
That means the owners of the building decided to leave the name on the window anyway. For that we thank them. The inscription adds character, though the neighborhood is not short on that commodity.
I like to think the new tenant occasionally wears a trench coat and a fedora and stops downstairs for a shot and a beer on a foggy night.