Why do you want to be able to tell what city the worker came from? In Civ 2, the unit-city identification was there since the cities supported the units, instead of the general empire supporting them like in Civ 3. And what do you mean by city screen? Do you mean the city status screen that you get when you double click on a city? If so, by "workers" do you mean "laboring citizens"? If so, you can move them around (make them work different squares than they already are) by clicking on a worked square, then a non-worked square. If you mean workers as in the units, then that makes no sense if by city screen you mean the city status screen, since units don't appear there (except for in the garrison box).