Any ballots delivered from the outside the precinct would have this feature.
We have already heard stories of trucks delivering thousands of ballots from outside the precincts in Detroit, Philadelphia, and Milwaukee.
In these cities there are many state representatives per city, so this would catch a whole bunch of fraudulent ballots easily.
This would also catch mass mail-in fraud where the fraudsters were sloppy.
Just because someone is a crook does not make them smart!
You’d think the fraudsters could get a sample ballot from the city needed, and make their fake ballots from that.
But I see what you are saying. It would be harder to get those and copy those from dozens of cities to make it look more legit. It would be easier to just manufacture fraudulent ballots from a few big cities but with the drawback of making it look less legit.