Well, it would probably fall under zoning/code enforcement.
My friend and I were just talking about this the other day. While both of our cities allow chickens he knows one of the city councilmen in the city he lives in and that person has told him that due to lack of funds (budget cuts) the cities really have no money to go and patrol little code violations like this. They just don't have a person to deal with it on the payroll right now. If it got to be a serious violation they would, of course, have to do something about it but if a neighbor calls and says "they have chickens and aren't supposed to" the city may not do anything - especially if your neighbor already has chickens.
I would just keep them and keep quiet about it.
No roosters, make sure there is no smell, etc. Don't give anyone a reason to not like your chickens.
In the meantime look into reading how you can change the zoning law to allow chickens. 