I rename the cities I want to be fortress and conclaves (Fort XXXXX, Conclave XXXXX), and let the rest to be towns. That is usefull for the begining, but once you have many cities, it is easy to forget renaming, and maybe you will change your idea (you find a better place for the fortress or conclave while the previous city is still growing). Anyway, I think you will not have many fortress if you want research and food. And if you want research, it is enough with the number of essence to determine if it deserves to be conclave or not.
But it is true that I miss having more information in the city popup, instead of renaming. A minimize option for the pop-up to be able to check the city would be appreciated too.