I was at a fine dining shop and I had two people present themselves as in charge.
1. He was wearing a three piece suit and it didn't come off the rack of the Men's Warehouse. He was doing everything from busing tables to refilling non bar drinks across the whole dining room. He did not appear to be doing table touches as a manager would and waited on every table he touched including refilling my drink.
2. He was much older than every other employee and was dressed in a comfortable pair of khakis and a loose button down shirt with the top three buttons open. He occasionally would randomly walk through the dining room and perform table touches and chat with what appeared to be regulars. I managed to get his name.
Sure enough, when I was fumbling with the mints at the front of the restaurant, I saw the business cards and without touching them I determined that #2 was the franchise owner and that left #1 to be the manager. I left #2 out of the report, as they don't want to read descriptions about themselves.
I have also had the manager wear the standard uniform at a fast casual before. For example, If they come to work wearing a grey shirt and it becomes soiled, they will have plenty of red shirts to change into in the back.
At another fast casual, the manager is often identified only by them performing manager type activities. The manager can be young and female. Never discount someone as being a manager because of age or gender. They are reaching manager status at a younger age than before.