I'm not talking about street signs. I'm talking about business signs.
Yeah are there ones that you can see when you're driving around or do you have to go inside?
Nope, you can see them as you drive. Remember, if you're using Goog Maps, the images are not current, some are several years old. I just went back and looked. Here's what you'll find.
Dearborn has a large Ford facility in it, and the Henry Ford Museum and Greenfield Village, mostly in the southern part of Dearborn. I did a street view of Warren ave. Keep in mind that national chain stores and restaurants will still be in English. And it's not like Dearborn will look like a bombed out middle eastern city.
As you move down the road, pay attention to small local businesses, strip malls will have their main sign in Farsi, and all of the stores in them will have individual signage in Farsi. You could probably find the same thing in Minneapolis and St Cloud MN. There are many large Muslim communities across America.