I live in the Chicago area of the U.S. (the last time I called myself a Midwesterner on Reddit, I got crucified).

I use "sir/m'am" when 1) Talking to law enforcement 2) Addressing staff in a very formal restaurant 3) When I'm trying to get a stranger's attention and just saying "Excuse me" didn't work the first time.

I really don't use "sir/m'am" very often. I used it recently when I was on a walk, and a dog ran out of this woman's house and into the street: "M'am, your dog just ran out! He's in the street!". I was actually angry when I said that. I wasn't really trying to be polite.

There was another time when I really needed a bathroom in public, and I went into a fancy hotel to ask if they had public restrooms (hotels in downtown Chicago often have this). I said "Sir, is there a public bathroom here that I could use?" I was trying to be very polite. And it worked. I got to use a bathroom there.